"I left my father and my grandmother. My grandmother refused to move and my father refused to leave his mother. I think they're going to die soon," said 20-year-old Boniface, walking into Goma some 10 km (six miles) from the volcano.

Trees caught alight and then crashed to the ground as winds fanned fires sparked by the lava from the 3,469-metre (11,380 ft) Nyiragongo volcano, creating a spectacular orange glow in a starless sky.

"I've never seen so much fire in my life. I look up at the volcano and all I see is burning trees and fire," said Karine Morency, a worker at a United Nations base in the Goma area.

"It's hard to imagine that nobody has been killed in the villages near the mountain. Everything smells like burning."

One villager said some people had suffered burns and were in need of medical treatment. "No one has done anything to help us yet. I'm asking the U.N. to help us," said Danny Engo, who said his house had been burned down.

Trucks, buses and cars crammed Goma's streets as residents sought to escape houses near the town centre, where witnesses said buildings were burning near the cathedral and soot filled the air and clung to clothing.

ASH AND LAVA

The ash and molten rock from the volcano swept to within one km (half a mile) of the U.N. base and Goma's airport.

By late afternoon, aid workers said lava flows had advanced around nine km (5.5 miles) since the eruption at 9:30 a.m. (0730 GMT) and that houses on the volcano's slopes were burning.

Morency said at least one village appeared to have been destroyed as had a road north to the town of Rutshuru. The lava flow was at least two km (1.2 miles) wide, she said.

A U.N. spokesman in Kinshasa said the world body had moved more than 400 staff to Goma town and was ready to retreat into neighbouring Rwanda if things got worse.

In 1977, scores died when a lake of lava burst through fissures in Nyiragongo's flanks at 60 km (40 miles) an hour, which experts said was the fastest lava flow on record.

"We're on red alert," Jean-Pierre Kisanga, spokesman for RCD rebels who control the town, told Reuters by telephone.

The Rwandan-backed RCD rebels control swathes of eastern Congo, but fighting with Congolese government forces has largely subsided since a peace process regained momentum last year.

The Nyiragongo volcano is one of eight on the borders of Rwanda, the Democratic Republic of Congo and Uganda.

Tropical rain forests and rare mountain gorillas are a feature of the area. A World Wildlife Fund official in Nairobi said the gorillas were unlikely to face any immediate threat.

Only two of the volcanoes are active - Nyamuragira, which erupted early last year, causing no casualties, and Nyiragongo.

While Nyamuragira is considered a potentially explosive volcano, Nyiragongo is a so-called "soft-lava" volcano, with a tube of lava that moves up and down inside its core.

Nyiragongo was last active in 1994, when a lava lake in its crater reappeared, casting an orange light onto clouds at night.