A bus collided with a truck on Kenya's main highway on Sunday, killing at least 22 people, police said.

The crash came three weeks after 17 people died in another accident along the same highway linking the capital, Nairobi, with the coastal city of Mombasa.

Some 24 others were injured in the Sunday morning crash and were receiving treatment, according to Paul Kisienya, the medical superintendent at Mtito Andei hospital that received most of those injured.

The passengers were returning to Mombasa after attending the funeral of their church pastor in western Kenya when the accident occurred.

A mother of two, Violet Mwandonyi, said the bus had just left Mtito Andei town, where the passengers had eaten breakfast.

"I cannot recall what exactly happened. The last thing I remember is that we were all wailing and calling on motorists to come to our rescue. I don't know the fate of my two children who were on the bus," she said.

The circumstances remain unclear but a passenger, Spenza Mudave said a truck hit the bus from behind, causing the bus to roll.

The National Transport Safety Authority had suspected that this was a case of "improper overtaking" due to the information gathered that the vehicles collided head-on.

Speeding and poor road conditions have previously been cited as contributing factors in road accidents in Kenya.