At least 27 people have died in Benin after a bus plunged off a bridge into the Oueme River, rescuers said on Tuesday, updating the toll from the weekend crash that left dozens missing.

The director of the West African country's civil protection agency, Abdel Aziz Bio Djibril, told local Bip Radio that rescuers retrieved 23 bodies from the bus pulled from the water and another three from the river, adding to the one person found dead on Sunday.

Nine survivors had been taken to hospital in a stable condition.

Three children were among the dead, according to the daily newspaper La Nation.

Sixteen people still missing

A civil protection worker, who asked to remain anonymous, confirmed the toll and told AFP the search was ongoing for 16 people who are still missing.

"The bus fell directly into the water but was not immediately submerged; all the people who could, struggled to get out of the water. Those who could not swim and tried to escape likely drowned... the bodies must have drifted a bit farther," Bio Djibril said.

The bus, managed by the company STM, departed from neighbouring Togo's capital Lome with 52 passengers.

The accident happened on the main Interstate 2 road, which crosses Benin from the economic capital Cotonou to Malanville in the north, on the border with Niger.