At least 38 people have died and scores were injured when two buses collided near the town of Kaffrine in central Senegal on Sunday, according to the president and the fire services.
In response to the "grave" accident, President Macky Sall announced three days of national mourning beginning Monday.
In a tweet Sunday he also said there had been 40 deaths and "many serious injuries".
"I am deeply saddened by the tragic road accident," he said on Twitter.
"I extend my heartfelt condolences to the families of the victims and wish a speedy recovery to the injured."
The Senegalese prosecutor said in a separate statement that 38 people had been killed.
Public prosecutor, Cheikh Dieng, said that early investigations suggested that the accident was caused when "a bus assigned to the public transport of passengers, following the bursting of a tyre, left its trajectory before colliding head-on with another bus coming in the opposite direction."
Colonel Cheikh Fall, who is in charge of operations for the West African country's National Fire Brigade, had earlier told AFP that 38 people had died and 87 were injured in the accident.
The accident took place around 3.15 am local time (0315 GMT) Sunday morning, Fall told AFP, adding that all the victims have been evacuated to a hospital and medical centre in Kaffrine.
The wreckage and demolished buses have since been cleared and normal traffic has already resumed on the road, he said.
The governor and local officials have already visited the scene, he added.
However this is one of the heaviest death tolls from a single incident in recent years.
Read more on FRANCE 24 English
‘Tirailleurs’: France’s forgotten colonial soldiers step out of the shadows
Senegalese MPs jailed for attacking pregnant legislator in parliament
A look back at the major African news stories of 2022