By Cyrus Ombati
The bus was speeding when its breaks failed before it rammed into other vehicles and a crowd at about 5.30 pm on Thursday.
There were fears the death toll could rise because of the nature of injuries those rushed to hospital sustained, police and witnesses said.
Police said dozens of people were rushed to hospital with multiple injuries.
The area is usually crowded during rush hours.
According to Nairobi Area Deputy Traffic Commandant Leonard Katana, the bus carrying passengers from the city centre.