Rescue and recovery operations are underway after a massive earthquake off the coast of Indonesia's island of Sumatra (search) triggered tsunamis that slammed into resort towns and seaside villages throughout southern and southeast Asia.

More than 11,000 people are dead in seven countries, and the number of casualties continues to rise.

The 9.0-magnitude earthquake, the largest recorded in the world in 40 years, occurred at sea shortly after 8 a.m. local Sumatra time on Sunday, or around 8:00 p.m. EST Saturday evening. Experts can't say whether it was the initial temblor or the nine aftershocks, including one on Sumatra's northernmost tip that measured 7.3 on the Richter scale, that sparked the tsunamis, or ocean surface waves, which reached as high as 20 feet.

The waves traveled more than 3,000 miles in all and at speeds that could have reached as much as 500 miles per hour, National Earthquake Information Center Scientist-in-Chief Harley Benz told FOX News.

The tsunamis hit Sri Lanka (search), India, Indonesia, Thailand, Bangladesh (search), Malaysia (search) and the Maldives.

Eyewitnesses said the massive waves dragged people out to sea along with cars, buildings and bridges.

"Initially we just heard a bang, a really loud bang," Gerrard Donnelly of Britain, a guest at Phuket island's Holiday Inn, told Britain's Sky News. "We initially thought it was a terrorist attack, then the wave came and we just kept running upstairs to get on as high ground as we could."

"People that were snorkeling were dragged along the coral and washed up on the beach, and people that were sunbathing got washed into the sea," said Simon Clark, 29, a photographer from London vacationing on Ngai Island.

Indonesia's National Earthquake Center said reports are difficult to get because communications in many of the areas are down. Indonesia's Vice President Jusuf Kawa said emergency operations are being put in place.

"We're sending our two top ministers to Aceh right now to access the latest situation. After that, we'll see what to do next. We're also preparing food supplies, medicines and makeshift shelters as emergency backup," he said.

In Sri Lanka, 1,000 miles west of the epicenter, many hotels and seaside restaurants were washed away along the flooded southern tourism belt. Around 1 million people were displaced from their homes, said Lalith Weerathunga, secretary to the Sri Lankan prime minister, and that does not include counts of areas in the northeast controlled by Tamil Tiger rebels.

The Sri Lankan Air Force has launched a rescue operation to airlift victims out of the area when they can't be reached by boat. International aid organizations are also mobilizing to bring, food, supplies and rescue workers to the devastated areas.

Freelance journalist Andrew Chant told FOX News that further tremors or tsunamis have not occurred since the original breakfast time catastrophe, but Thai authorities are telling people to stay away from the coasts, and many have moved up into the mountains for fear of another tsunami (search).

"A lot of the tourists we've spoken to are utterly traumatized and don't want to stay near the coast anyway. I have spoken to some who have gone up a hill and they're basically going to stay under trees the whole night," Chant said.

President Bush was briefed about the disaster while traveling from Camp David, Md., where his family spent Christmas, to his ranch in Crawford, Texas. White House Deputy Press Secretary Trent Duffy said the United States "stands ready to offer all appropriate assistance" to the nations most affected, inlcuding Sri Lanka, the Maldives, Thailand and Indonesia.

"On behalf of the American people, the president expresses his sincere condolences for the terrible loss of life and suffering caused by the earthquake and subsequent tsunamis in the region of the Bay of Bengal," Duffy said in a written statement.

"Certainly, our thoughts and prayers are with those families and loved ones who have experienced a loss of life," Duffy told reporters traveling aboard Air Force One.

The State Department told FOX News on Sunday afternoon that two Americans were killed in Sri Lanka, one was killed in Thailand and several other Americans were hurt. The diplomatic agency continues to check with its embassies, which are locating expatriates and tourists who registered with consular offices.

Pentagon Duty Officer Cheryl Irwin told FOX News that the National Military Command Center has received no reports of any damage to the Diego Garcia Naval Support Facility, off the southern coast of India. The Navy is considering whether and what kind of aid to offer to local governments in the region, said Navy Press Duty Officer Lt. Pauline Pimetel.

Since this is peak tourist season in Southeast Asia, and a frequent time for holidays by Americans and Europeans, many countries can expect casualties to be reported.

The Thai Foreign Ministry said it had not issued numbers of foreigners missing, injured or dead, but they include nationals of South Korea, Japan, Germany, South Africa, Hong Kong, Britain, Denmark, Australia, Malaysia, Mexico, Russia, Sweden and the United States. The governor of Phuket, the most heavily visited tourist destination in the country, said the grandson of the king of Thailand is also listed among the missing.

"I am afraid that there will be a high figure of foreigners missing in the sea and also my staff," said Chan Marongtaechar, owner of the PP Princess Resort and PP Charlie Beach Resort, on Thailand's Kho Phi Phi island, where "The Beach" starring Leonardo DiCaprio was filmed. Officials said they are trying to evacuate 600 tourists and residents from that island.

Early reporting showed 3,000 dead in Sri Lanka, 4,185 in Indonesia, and 2,300 along the southern coasts of India. At least 289 were confirmed dead in Thailand, 42 in Malaysia and two in Bangladesh.

The pro-rebel www.nitharsanam.com Web site reported about 1,500 bodies were brought from various parts of Sri Lanka's northeast to a hospital in Mullaithivu district. That number included 170 children in an orphanage.

Hundreds of bodies were found on various beaches along India's southern state of Tamil Nadu, and more were expected to be washed in by the sea, officials said. A group of 32 Indians — including 15 children — were killed while taking a ritual Hindu bath to mark the full moon day.

"I was shocked to see innumerable fishing boats flying on the shoulder of the waves, going back and forth into the sea, as if made of paper," said P. Ramanamurthy, 40, who lives in Andra Pradesh's Kakinada town in India. "I had never imagined anything like this could happen."

Health ministry official Els Mangundap said 1,400 of the people dead in Indonesia were located in the Aceh provincial capital, Banda Aceh.

Relatives went through lines of bodies wrapped in blankets and sheets, searching for dead loved ones. Aceh province has long been the center of a violent insurgency against the government.

In the Maldives, authorities shut down the only international airport, stranding tourists. One report from the islands said a British tourist died from a heart attack, possibly caused by seeing the huge wave heading toward him.

"All the planet is vibrating" from the quake, said Enzo Boschi, the head of Italy's National Geophysics Institute. Speaking on SKY TG24 TV, Boschi said the quake even disturbed the Earth's rotation.

The U.S. Geological Survey geophysicist Julie Martinez said the earthquake was the world's fourth-largest since 1900 and the largest since a 9.2 temblor hit Prince William Sound Alaska in 1964. Another official from USGS said that a warning center could have saved most of the thousands killed. He said none of the countries hit had a tsunami warning system to alert people. Tsunamis in the Indian Ocean are rare.

Indonesia, a country of 17,000 islands, is prone to seismic upheaval because of its location on the margins of tectonic plates that make up the so-called the "Ring of Fire" around the Pacific Ocean basin.

The Indonesian quake struck just three days after an 8.1 quake struck the ocean floor between Australia and Antarctica, causing buildings to shake hundreds of miles away but no serious damage or injury.

Quakes reaching a magnitude 8 are very rare. A quake registering magnitude 8 rocked Japan's northern island of Hokkaido on Sept. 25, 2003, injuring nearly 600 people. An 8.4 magnitude tremor that stuck off the coast of Peru on June 23, 2001, killed 74.

FOX News' Julie Kirtz and Sharon Kehnemui Liss and The Associated Press contributed to this report.