Five people were found choked to death on toxic fumes from the volcanic eruption in the Democratic Republic of Congo's Nyiragongo volcano Monday, as strong aftershocks rocked the city of Goma.

The deaths bring to 20 the number killed since Africa's most active volcano erupted Saturday, spewing red-hot molten lava that engulfed houses in its wake. "We have just discovered five dead people," civil society leader Mambo Kawaya told Agence France-Presse (AFP), saying that they were "asphyxiated by the gas" as they tried to cross the cooling lava some 13 kilometers (8 miles) north of Goma.

A sixth person is in a "critical state with trouble breathing and has been taken to hospital," Kawaya said.

Goma, a city of some 1.5 million people in the shadow of the volcano and on the shores of Lake Kivu, was on edge as violent aftershocks continued through the night and into Monday.

"They're multiplying and they come at any moment," one resident told AFP, describing the aftershocks as "very worrying and that the night was long – there is fear in our stomachs," she said. Several strong aftershocks were also felt in neighboring Rwanda Monday, including a 5.1-magnitude earthquake under Lake Kivu in the Rubavu district at 8:37 a.m. GMT, the Rwanda Seismic Monitor (RSM) said.

A 4.5 magnitude quake followed at 11:53 a.m. GMT, the RSM said on Twitter, adding that the tremors were being "produced by vibrations generated by the movement of magma within the volcano." Tens of thousands of residents had fled the city in panic – around 7,000 of them to Rwanda – when Nyiragongo began erupting Saturday evening.

Along with the five people found dead Monday, at least 15 other people have died, although most were not killed directly by the eruption. Authorities said nine people died in accidents during the rush to evacuate, while four prisoners were killed while trying to escape in the melee. Two people were found burned to death. Officials said 17 villages on the city's fringes had suffered major damage.

Schools shut, electricity cut

While the river of lava stopped at the edge of Goma and many residents have now returned, each aftershock brought anxious residents back out onto the streets Monday.

"We just had a big aftershock – I'm scared to stay in my office," said a resident who gave her name only as Deborah, an employee at an international organization, reached by telephone. "I'm wondering if I should stay or go home. The electricity has cut out," she said.

Schools are still shut with pupils told to stay at home, although businesses and petrol stations were open again. Nyiragongo's last major eruption, in 2002, claimed around 100 lives.

Hundreds homeless

By Monday the blackish solidified lava was still hot and smoking, with dozens of people turning out to inspect it or even walk on it, despite the risk of inhaling toxic fumes. The volcano appeared calm on the horizon, with the usual smoke rising from its crater.

A government delegation including seven ministers arrived from Kinshasa early Monday, while President Felix Tshisekedi has cut short a European tour to supervise the aid operation. Health Minister Jean-Jacques Mbungani said upon his arrival in Goma that the delegation was set to organize support for people made homeless after the eruption after "assessing the state of affairs." Hundreds of people spent Monday night in the street after the lava destroyed their homes.

Government spokesman Patrick Muyaya warned Sunday that the prices of food and other essentials are set to rise in Goma as the eruption has cut off several hundred meters of the road to Butembo, the region's main trade route. After taking part in a United Nations reconnaissance flight over Nyiragongo, volcanologist Kasereka Mahinda said it was uncertain why the aftershocks were continuing and whether the volcano's burst of activity was finished.

"Because of the fog we were unable to see the inside of the crater," said Mahinda, the scientific director of the Goma Volcanology Observatory. "If there is lava in the crater, the fracturing caused by the movement of the earth would represent new activity," he said. "If there is no lava in the crater, then these earthquakes are happening because the earth is in the process of refinding its balance."