Mount Nyiragongo in the Democratic Republic of Congo (DRC) erupted for the first time in nearly two decades. Lava slid from the slopes to the eastern city of Goma, forcing thousands of people to flee.

The red light of Mount Nyiragongo illuminates the night sky above about 2 million lakeside cities. On Saturday, Goma residents with mattresses and other items fled the city on foot-many toward the border with Rwanda go ahead.

Nyiragongo’s last eruption in 2002 killed 250 people and left 120,000 homeless in the Democratic Republic of Congo. It is one of the most active volcanoes in the world and is considered one of the most dangerous.

A source told Reuters on Sunday that traces of lava extracted from the volcanic eruption appeared to have stopped a few hundred meters from the edge of the city.

Rwanda’s Ministry of Emergency Affairs said more than 3,500 Congolese had crossed the border. Official Rwandan media said they will be placed in schools and places of worship.

Volcano observers have been concerned that the volcanic activity observed in Nyiragongo in the last five years is similar to the situation before the eruption in 1977 and 2002.

Ever since the World Bank cut funds amid allegations of embezzlement of public funds, volcanologists monitoring Nyiragongo’s OVG have been conducting basic checks on a regular basis.