— Flights were severely backed up at Nairobi’s main international airport late Wednesday after a massive pre-dawn fire engulfed the facility, the gateway to one of sub-Saharan Africa’s most vital trading regions, and forced its closure.

By evening, the airport had reopened for domestic and cargo flights, but international flights had not resumed. Kenyan officials said they planned to temporarily convert a domestic unit into an international terminal in an attempt to end the backlog.

There were no immediate reports of injuries from the blaze, which started about 5 a.m. in Jomo Kenyatta International Airport’s arrivals and immigration area, authorities said.

“It looked like the entire terminal would be gone,” said Katie Price, an aid worker with ­Baltimore-based Catholic Relief Services who arrived on a flight from Malawi about 5 a.m.

Hundreds of passengers were stranded outside the airport building as firefighters, reportedly hampered by a lack of functioning equipment, battled intense flames and billowing smoke.

The cause of the fire was not known. Security officials in Nairobi have been on high alert in recent days because of intercepted intelligence suggesting a possible attack on Western targets in the Middle East or Africa, as well as the anniversary Wednesday of the 1998 bombings of the U.S. embassies in Nairobi and Dar es Salaam, Tanzania, which killed a total of 224 people.

Boniface Mwaniki, head of Kenya’s anti-terrorism operations, told the Associated Press earlier Wednesday that he was waiting for the fire to be extinguished so he could inspect the scene before attempting to determine the cause.

One potential motive for arson is a recent dispute between officials of the Kenyan airport authority and owners of duty-free shops at the facility. Some of the shops were forcibly closed after a lease agreement expired.

Witnesses said firefighters arrived on the scene late and appeared hobbled by a lack of equipment. As of last month, Nairobi County’s fire department did not have a single working fire engine, the Daily Nation newspaper reported at the time, having auctioned off three engines to pay a $1,000 repair bill.

“It is a disgrace of biblical proportions that the entire Nairobi County does not have a public fire engine in working condition,” the paper wrote in an editorial. As government officials debated whether to buy new engines or repair old ones, the editorial scolded, they set aside money “to build mansions for governors, big vehicles for county executives and other needs without a direct benefit to Kenyans.”

Michael Kamau, the country’s transportation and infrastructure secretary, said that the fire had started in a central part of the airport and that “this made access difficult.” Local television images showed the terminal’s interior gutted and blackened and the roof partly caved in.

The disruption of one of East Africa’s busiest airports will be a substantial blow to Kenya’s economy and the entire region, with a ripple effect felt around the globe. The nation supplies a third of the flowers sold in Europe, transporting them out of the airport and generating $1 billion annually in foreign exchange. Also, August is the height of tourism season, a core source of foreign revenue.

Price, the aid worker, said that upon landing, passengers were told there was a “small fire” at the airport and that they needed to remain on the plane. Two hours later, she and hundreds of passengers were still on the tarmac “watching the fire get bigger and bigger,” she said.

“Everyone remained pretty calm, until [airport staff] alerted us that a fuel line was underneath a part of the terminal,” Price said. “They evacuated the planes and the passengers to the cargo area.”

After several more hours, she and thousands of other passengers were allowed to leave the airport through a makeshift terminal.

Immigration officers typically take fingerprints and photos of arriving passengers, a security precaution in a part of the world where al-Qaeda-linked militants remain active. But Price said none of the passengers was screened before being given stamps to enter the country.

Given the damage to the terminal, it is highly likely that the facility’s security infrastructure was destroyed, including passport records. Price, who was staying in a downtown hotel waiting to travel to Congo, said she was not told when she could proceed.

“There are just hundreds, thousands, of passengers waiting to fly to other cities in Africa,” she said.