A fire engulfed Kenya’s main airport on Wednesday, choking a vital travel and trade gateway to east Africa, witnesses and officials said.

Firefighters struggled to contain the blaze at Jomo Kenyatta International Airport in Nairobi, the region’s busiest, that started early in the morning in the immigration section of the departure lounge and spread to the international arrivals area, officials said.

Huge plumes of black smoke billowed from the airport buildings, but there were no immediate reports of casualties.

The cause of the fire was not yet known.

“We are still fighting to contain the fire. Investigations will start immediately after,” Michael Kamau, cabinet secretary for transport, told reporters at the airport.

“The fire started at a very central part of the airport and this made access difficult. But we have closed the airport indefinitely as we try to contain the fire.”

Hundreds of passengers were stranded outside the airport, which was cordoned off to keep the public out.

“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 had been heightened at the airport after the fire started.

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, said on its Twitter feed 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 neighboring countries including in Uganda, Tanzania and Rwanda.