A RUNAWAY tanker carrying volatile gas has slammed into other vehicles and burst into flames on a major road in Kenya, killing at least 39 people and injuring 10, officials said on Sunday.

The tanker lost control while going downhill on the road from the capital Nairobi to Naivasha late on Saturday, said Mwachi Pius Masai, the deputy director and communications officer for the National Disaster Management Unit.

"This is a serious chemical incident," Mr Masai said. "Police and other rescuers are still on the scene ... clearing debris."

The original death toll was 33 but has risen to 39. Officials said it could still rise further.

Eleven vehicles were burnt out. Witness Peter Kimani said: "The lorry was in high speed and lost control after hitting speed bumps and ended up ramming into oncoming cars."

Kenyan President Uhuru Kenyatta issued a statement on Sunday calling the incident "a grizzly and unnecessary accident. The tanker responsible for the deaths should not have been on that particular road at that hour."

The president urged "the agencies responsible for enforcing traffic regulation to fully investigate this tragic breach."

Mr Kenyatta said that 11 of those killed were officers from the General Service Unit who provide VIP protection, including to the president.

Kenya has struggled to reduce the rising number of road accidents as more people acquire vehicles in a growing middle class.

In 2013, the government reintroduced breathalysers to limit accidents blamed on drink-drivers.

According to the National Transport and Safety Authority 1,574 people died in road accidents in the first half of this year, 86 more than in the same period last year.

AP