Traffic Commandant Samuel Kimaru said several other people who were injured were taken to hospital by motorists and their condition remained unclear.
“We have confirmed the deaths of four people who died on the spot for now,” Kimaru told Capital FM News on telephone soon after the accident.
He however said witnesses had informed police that some of those taken to hospital had suffered serious injuries, raising fears of a possible death toll increase.
“We don’t know their condition. We have sent our officers to various hospitals to check and take their details,” he said. “We do not know much about their condition at the moment.”
Nairobi Deputy Traffic Commandant Leonard Katana described the accident as “horrific.”
“We have been told there are people dead and others seriously injured. I am rushing to the scene,” he said.
There were conflicting reports on the number of the dead, with some witnesses putting the toll at as high as 10 while others said they had seen eight bodies at the scene.
“People can say anything. What we know is that there are four people who died on the spot. We are yet to get the other details, because we don’t know the condition of those taken to hospital,” Kimaru said.
Kenya’s road safety record has worsened lately, with road accidents having killed about 2,000 people since January.
National Police Chief David Kimaiyo has directed traffic police officers to be strict while enforcing traffic regulations on the road.