Nairobi airport fire in pictures
There were no initial reports of casualties in the blaze at Jomo Kenyatta International Airport, but an official said on Wednesday the fire was "massive", adding that the arrivals and immigration sections were "totally damaged".
Images on Kenyan media showed flames rising high in the sky and billowing clouds of black smoke out of the main arrivals and departures terminal, with dozens of police and fire trucks at the scene.
Firefighters were tackling the blaze, while flights were being diverted to other airports, the interior ministry said in a statement.
The fire comes less than 48 hours after a fuel jet pump failure caused huge delays at the airport.
Kenya Airways, one of the leading airlines in the region which uses the airport as its main hub, on its Twitter page said that it was diverting flights to Kenya's port city of Mombasa and that transit passengers were being taken to hotels.
Other airlines are expected to divert flights to Mombasa and to neighbouring countries including in Uganda, Tanzania and Rwanda.
"People should not come to the airport while this work is ongoing. No casualties have been reported and the fire fighters are doing a good job. Safety is paramount," Cabinet Secretary for the Interior Joseph ole Lenku said, adding that security was heightened at the airport after the fire started.