NAIROBI (REUTERS) - Kenya said that it would restart domestic flights and international cargo flights later on Wednesday after the country's main airport was shut following a fire earlier in the day.

"We expect cargo and domestic services to resume from this airport this afternoon. They will operate from the cargo terminal," said Mr Manoah Esipisu, spokesman for the presidency.

Kenya's Jomo Kenyatta International Airport is a vital travel and trade gateway to east Africa.

Flames from the inferno lit up the early morning sky, and the intense heat repeatedly drove back firefighters. A huge plume of black smoke billowed from the airport buildings, but there were no immediate reports of casualties or injuries.

Hundreds of passengers were stranded outside the airport which was cordoned off to keep the public out after the fire started in the arrivals and immigration area, officials said.

The cause of the worst fire in record at east Africa's busiest airport was not yet known.

One passenger at the airport said he heard two small explosions from the international arrival area, then sirens.

"I was waiting for my flight around 5 am when I heard two explosions, as if from gas cylinder or electricity fault," said the passenger, a Kenyan who requested anonymity.

"Within minutes, the entire airport was secured by police and Kenya airport authority personnel, who ordered everybody out of the airport," he said.

The airport buildings were ravaged by the fire. Television pictures showed desks that had been reduced to chacoal inside the burned out terminal. The roof had partly caved in, and the floor was flooded with water from fire fighters.

Stranded passengers watched from a short distance as grey smoke billowed from the blackened building. Many sat on their bags or on the ground as they waited for information.

Mr Svein Huseby, 38, an engineer from Norway, had been due to fly home after visiting his Kenyan girlfriend.

"It's been chaotic ... No one knows if they will be going home in two hours, two days or two months. People are going crazy," he said. "Some official information would have been nice."

Exporters of perishable produce, mainly flowers, said the impact of the fire would cripple their business.

"This is disastrous," Ms Jane Ngige, chief executive officer of exporters association Kenya Flower Council, told Reuters.