Residents of the DR Congo city of Goma were told to evacuate Thursday as officials warned that the nearby Mount Nyiragongo volcano might erupt for a second time at any moment.

Constant Ndima Kongba, the military governor of the North Kivu province, said magma was detected underneath the city and adjoining Lake Kivu, citing seismic and ground deformation data. The molten rock that erupts from volcanoes normally stays below the earth's crust.

"Given these scientific observations, an eruption on land or under the lake cannot be ruled out at present, and it could occur with very little or no warning," said Kongba.

The volcano is about 6 miles (9.7 kilometers) north of Goma, home to more than 600,000 people. A total of nearly 2 million people live in Goma's greater urban area.

Thousands flee, roads 'very congested'

The strato-volcano, which is nearly 3,500 meters (11,500 feet) high, erupted over the weekend, killing at least 31 people and leaving 20,000 homeless. Another 40 people are still missing from Saturday. Hundreds of aftershocks followed, destroying more buildings in the process.

Omar Abood, chief of the UN peacekeeping mission in Goma, told DW that tens of thousands of people have fled since early in the day.

"They've been going in different directions, mainly either to the Rwandan border on the eastern ide of Goma or towards the west – towards an area called Sakey," said Abood, adding the "roads are still very, very congested."

Mount Nyiragongo is Africa's most active volcano. Before last Saturday, Nyiragongo last erupted in January 2002, killing more than 100 people and covering almost all of eastern Goma with lava, including half of the airport's landing strip. More than 100,000 were left homeless in the aftermath.

"The first time there was an eruption we lost everything, today we still take the same road as in 2002," Suzana Komayombi told AP.

More than 600 died in the volcano's deadliest eruption in 1977. Nearby Nyamuragira, which scientists are also monitoring, is also highly active. Its last major eruption was a decade ago.

Potential 'limnic eruption'

Experts monitoring the volcano were reportedly concerned hat there may be a "limnic eruption," where volcanic activity combines with a nearby lake to spew out lethal levels of carbon dioxide gas.

An eruption of this kind occurred in Cameroon in 1986, which killed more than 1,700 people and thousands of cattle. Dissolved carbon dioxide (CO₂) in the depths of the lake had erupted and formed an invisible cloud that was then moved by the wind.

Should a limnic eruption occur, it would require lava to flow from Nyiragongo to combine with volcanic activity underneath Lake Kivu, and form a "fissural or phreato-magmatic eruption under the lake and/or a large earthquake of 6.5 or 7 magnitude," said the Goma Volcano Observatory (OVG) in a technical note cited by the AFP news agency.

The OVG said the limnic eruption, the worst of several possible scenarios, means that "dissolved gas in the lake's deep water would rise to the surface, especially the CO2, asphyxiating all living beings around Lake Kivu on the Congolese and Rwandan side," which could lead to "thousands of deaths."

kbd/dj (AFP, AP, Reuters, dpa)