The cruise ship railing over which an Australian couple fell into the ocean was higher than industry regulations required and was designed to prevent accidental falls, a spokeswoman for the cruise company said Friday as an intense search continued for the missing passengers.

Paul Rossington, a 30-year-old paramedic, and his 26-year-old girlfriend Kristen Schroder, both from the town of Barraba in New South Wales state, were discovered missing Thursday morning after the Carnival Spirit docked at Sydney's Circular Quay at the end of a 10-day journey, New South Wales Police Superintendent Mark Hutchings said.

Stephen Leahy, head of Westpac Life Saver Rescue Helicopters, said that if the couple fell accidentally, they could have survived, noting that the ocean was calm and fairly warm, and describing Rossington, a paramedic for the state ambulance service, as very fit. "He has a very good understanding ... of survival techniques and his level of fitness will help him," Leahy told Australian Broadcasting Corp. "He'll also be able to help his partner. The chances of two young people surviving are very, very good, and certainly from our perspective, we haven't given up hope."

Surveillance camera footage showed the couple was outside their cabin when they fell more than 20 meters (65 feet) from the ship's mid deck Wednesday night, Hutchings said. At the time, the ship was about 120 kilometers (65 nautical miles) off the coast of Forster, a city 300 kilometers (185 miles) north of Sydney.

Carnival Spirit is owned by Miami-based Carnival Corp., the world's largest cruise operator. Carnival Corp.'s representative in the South Pacific region, Ann Sherry, chief executive of Carnival Australia, said the railing over which the couple fell was 5 centimeters (2 inches) higher than industry safety regulations mandate.

"It's designed really to prevent accidental tripping" overboard, she told reporters.

"We want to make sure that it's not possible for people to fall overboard or to trip and fall overboard ... so I think it would be highly unlikely, but again, in this case, the police are conducting a full investigation," she said.

Rescue officials searched through the night with heat-seeking infrared equipment, but had not found the couple as of Friday afternoon, police said.

"I do have grave concerns for them.... whilst we hold out some hope, the hope is fading, unfortunately," Hutchings told reporters.

Investigators were having the surveillance video enhanced in a bid to determine whether Rossington and Schroder jumped or fell by accident. The video shows the pair went over the railing around the same time, with a brief pause between them, Hutchings said. It is not clear from the footage who went overboard first.

Police were also questioning family, friends and passengers in a bid to find out what happened. "The footage alone won't tell the whole story," Hutchings said.

No life preservers were missing from the ship, Hutchings said. A missing life preserver might have indicated that one of the missing passengers had attempted a rescue.

The ship has around 600 surveillance cameras that are constantly monitored, although no one reported seeing the fall at the time. Sherry defended the level of monitoring of passengers aboard the ship that allowed the couple's fall to go unnoticed. At least four people were monitoring the ship's surveillance cameras at any time, she said.

The night Rossington and Schroder vanished, the video surveillance staff was busy watching the public areas of the ship, she said.

"It was the last night of a cruise," Sherry said. "Virtually everybody else was in the public spaces on the ship, and they're the areas that we focus on in those times."

Andrea Hayward-Maher, spokeswoman for the Australian Maritime Safety Authority, which is coordinating the search, said five airplanes and a helicopter were searching a 700-square-kilometer (200-square-nautical mile) area of sea 110 kilometers (70 miles) east of Forster. She said search conditions were good.

The couple and seven of their family and friends were among 2,680 passengers on a South Pacific cruise. The ship's last stop was Mare Island in New Caledonia, which it left on Monday, bound for Sydney.

The emergency is the latest high-profile problem for Carnival Corp.

Last year, the Costa Concordia ran aground off the coast of Italy, killing 32 people. Also last year, the Costa Allegra caught fire and lost power in the Indian Ocean, leaving passengers without working toilets, running water or air conditioning for three days. Costa is a division of Carnival Corp.

In February, passengers aboard the Carnival Triumph spent five days without power in the Gulf of Mexico after an engine-room fire disabled the vessel. Those on board complained of squalid conditions, including overflowing toilets and food shortages.