A river of lava flowed through the center of Goma on Saturday and burned everything in its path, killing up to 40, creating a five-foot-high wall of cooling stone and leaving a half-million people homeless.

The 130-foot-wide path of molten rock made a fishhook pattern as it rolled down Mount Nyiragongo, 12 miles north of Goma, passed through the central business district and flowed into Lake Kivu, sending sulfuric smoke and steam into the air.

Later Saturday lava began pouring out of what appeared to be a new fissure, 6 miles east of Nyiragongo, authorities said.

Many of those left homeless fled east into neighboring Rwanda.

U.N. officials reported at least 40 deaths. Hospital officials in Gisenyi, Rwanda, recorded 16 deaths but said a definitive count was not possible because of the chaos.

Dr. Cedrique Abeli of Gisenyi Hospital said the 16 dead included two infants and two elderly burn victims.

Abeli and four colleagues struggled to treat the injured as hospital wards filled with dozens of burn victims and women who suffered miscarriages from stress.

Dawn broke in Gisenyi with the sound of hundreds of crying, hungry children. Refugees bathed in the lake, the water putrid from the lava.

"There is no food, no water, no sanitation. We are here like animals," said Richard Mwambo, a teacher who fled Goma and was preparing to board a dangerously overcrowded ferry to Bukavu, a four-hour trip down Lake Kivu. "(We are) afraid of dying. If we are to die, it is better to die in Congo, not Rwanda."

Maj. Pierre Pinchart, the military attache at the Belgian embassy in Kigali, Rwanda, said the situation could become a major humanitarian disaster, with two infants already dead from starvation and dehydration. He said Goma's water purification system had been destroyed and refugees were drinking lake water, which could trigger a cholera epidemic.

"The lake water is poison, because everything from the city is going in the lake," Pinchart said.

A Belgian relief plane would bring water purification systems to Gisenyi on Sunday, he said.

British Foreign Secretary Jack Straw and French Foreign Minister Hubert Vedrine will visit refugees when they travel to Rwanda next week, part of a previously planned trip to central Africa. Earlier Britain pledged nearly $3 million in emergency funding for volcano victims.

More than a dozen earthquakes shook the region every hour, some of them severe enough to send people running into the street in panic. Hundreds of thousands of Goma residents, ordered to abandon their impoverished city as it burned, slept outdoors in Gisenyi, seeking shelter under porches.

More than half of Goma was consumed by lava. A fire crackled at the art deco Black and White Dance Club and propane gas tanks exploded throughout the town. Only a handful of police patrolled the otherwise empty city.

The night sky glowed scarlet from the fires, and international aid workers withdrew 30 miles from the city out of fear that large quantities of methane gas existing naturally in the lake would explode or bubble up, killing people close to shore.

Stephen Johnson, of the U.N. office for the coordination of humanitarian affairs, said from New York there were no indications that the eruptions which began Thursday had finished.

He said about 200,000 people fled west into Congo, while 300,000 others crossed over to Rwanda in the east. The lava cut the only road connecting the two sides.

Damascene Ntiruhungwa, the Rwandan interior minister, said officials would meet with U.N. personnel Saturday. Two camps have been set up in the northwestern corner of Rwanda to house the displaced, but Congolese are loath to be seen as refugees in Rwanda, preferring nearby Congolese cities like Bukavu.

Adolphe Onusumba, head of the Rwandan-backed rebels controlling the Goma region, implored residents not to return to their homes.

"We are declaring a state of emergency and urge people not to return to their homes because of the losses," he said in a radio broadcast from the devastated city.

Nonetheless, hundreds of residents returned Saturday morning. Some shops located on high ground were open, selling food or pharmaceuticals. There were scattered reports of looting.

Residents who found their homes intact said they planned to move back.

Brian Baptie, a volcano seismologist at the British Geological Survey in Edinburgh, Scotland, said Nyiragongo is one of the most active volcanos in Africa.

"Although the lava moves quite fast going down the flanks, once on flat land it moves quite slowly so people can get out of the way if they have warning," he said. "It's the refugee problem created that's the big cause for concern."

The United Nations has sent several thousand military observers and peacekeepers into Congo following a cease-fire in the civil war that started in 1998 in Goma.

A U.N. official who evacuated civilian and military staff from Goma to Kigali said the deputy force commander, Gen. Roberto Martinelli, arrived there Friday and would travel to Gisenyi and Goma on Saturday to assess the situation.

Britain will give $2.9 million to help victims, with $1.4 million already allocated to humanitarian agencies in Congo, International Development Secretary Clare Short said.

The 11,381-foot Nyiragongo and 10,022-foot Nyamulagira volcanoes are the only active ones in the Virunga chain of eight volcanoes running east into Rwanda. Nyiragongo last erupted seriously in January 1977.