As the red glow of Mount Nyiragongo tinged the night sky above the lakeside city of about 2 million, thousands of Goma residents carrying mattresses and other belongings fled the city on foot - many toward the frontier with Rwanda.
Nyiragongo's last eruption in 2002 killed 250 people and left 120,000 homeless. It is one of the world's most active volcanoes and is considered among the most dangerous.
Rwanda's Ministry in Charge of Emergency Management said more than 3,500 Congolese have crossed the border. Rwandan state media said they would be lodged in schools and places of worship.