At least 35 people have been killed in a bus crash near Mwingi town in eastern Kenya, a traffic officer has said.
Most of the passengers worked in the capital, Nairobi, and were returning to their homes to vote in Monday's election, a survivor told the BBC.
Farah Aden Ali, who sustained minor injuries, said the bus over-turned after the driver lost control.
Many of Kenya's roads are in a bad state, and buses are poorly maintained, correspondents say.
Traffic officer Samuel Kimaru said at least 35 passengers died and another 50 were wounded in the overnight accident.
"The death toll may increase because there were serious injuries following the accident. Those who were injured are undergoing treatment in hospital," he is quoted as saying by Kenya's Standard newspaper.
Mr Aden Ali told the BBC Somali Service that rescue teams arrived only about four hours after the crash, causing many people trapped in the wreckage to die.
The bus was over-crowded with many passengers - who were going to the towns of Mandera and Garissa - standing, he said.
"The bus had problems with the gear from when it left Nairobi," Mr Aden Ali added.
He said he was asleep, but woke up shortly before the accident.
"The driver lost control. He tried to bring it back under control, but it rolled over and turned on its side," Mr Aden Ali said.
Traffic on Kenya's roads is usually high before an election, as city workers travel to their rural homes, where they are registered to vote.
Kenya will hold parliamentary and presidential elections on Monday.
The presidential poll is expected to be a close contest between Prime Minister Raila Odinga and one of his deputies, Uhuru Kenyatta, who is due to stand trial at the International Criminal Court (ICC) later this year for allegedly orchestrating violence after the disputed 2007 election.
President Mwai Kibaki, who beat Mr Odinga in the 2007 election, is stepping down after two terms.