A second passenger boat has sunk in a Congolese river, leaving up to 70 people dead. It happened just one day after another vessel caught fire and 200 passengers were believed to have drowned.

The latest riverboat disaster happened in northwest Congo early Sunday, when the vessel struck a rock. Authorities say 15 people survived.

On Saturday night, a boat laden with fuel and passengers set fire and capsized in Congo's Kasai River, with one survivor warning that as many as 200 people may have been killed.

Survivor Fabrice Muamba said the boat's engine caught fire Saturday night just as it was passing by the village of Mbendayi, about 70 kilometers from the town of Tshikapa.

Muamba estimates he was one of only 15 people who managed to jump off the sinking boat and swim to safety.

He said the vessel was also carrying drums of fuel at the time of the fire.

Another survivor, Romaine Mishondo, told The Associated Press the boat was packed with so many passengers it reminded her of "a whole market in the village full of people."

Mishondo said that when the fire broke out and passengers jumped into the river, nearby fishermen refused to help them.

"Fishermen attacked the boat and started beating passengers with paddles as they were (trying) to loot goods," she said. "The fishermen refused save passengers, instead taking goods into their pirogues. ... I survived because I hung onto a jerrycan until another vessel passed by the scene and rescued us."

Two sailors aboard the sunken boat have been arrested and an investigation into the disaster is underway, said local official Francois Madila.

Madila said it appears the list of passengers may have been destroyed in the fire and the detained sailors have not revealed how many people were on the boat.

While Congo has had numerous deadly boat incidents in the past, Saturday's disaster was the deadliest this year.

In May, a canoe overturned in eastern Congo and dozens were killed.

That followed an incident the previous November when at least 90 people died when a logging-boat sank in eastern Congo. It was not supposed to be carrying passengers.

Because Congo has a high concentration of jungle territory and only 480 kilometres of paved road, people often travel by boat even if they cannot swim.

Passengers are often put at risk by boat operators who put too many people on their vessels.

With files from The Associated Press