Air travellers are stranded at Suvarnabhumi airport on Thursday after Pakistan closed its airspace on Wednesday. (Photo by Varuth Hirunyatheb)

Some 4,900 passengers were stranded at Suvarnabhumi airport on Thursday due to the temporary closure of airspace over Pakistan which snarled regional air traffic, especially between Asia and Europe.

Suvarnabhumi general manager Suthirawat Suwannawat said 4,000 of them were Thai Airways International travellers.

As of 1pm on Thursday, 16 inbound and 20 outbound flights were cancelled, while three flights returned on Wednesday after departing the airport, Wg Crd Suthirawat said.

THAI resumed flights to Europe on Thursday by rerouting to Chinese airspace. The airline is trying to send passengers stuck at the airport to their destinations through its allied airlines and on three planned special flights.

The flight resumption has reduced to 3,000 the number of THAI passengers waiting to leave the international gateway, according to Thera Buasri, director of THAI's Ground Operations Control Department.

"It's now down to 3,000 [stranded passengers]," he said. "We expect to take no longer than three days to send them all to their destinations," he said.

The terminal at Suvarnabhumi was so crowded that Immigration Bureau chief Pol Lt Gen Surachate Hakparn, tweeted a warning to "Please spare your time for your trip!''

The disruptions marked an unhappy end to a month-long tropical holiday for a group of 25 Danish students unable to board a connecting flight in Bangkok.

"The guard over there just said we have to go down to the basement to sleep. So we can't get any help or information,'' Sara Bjerregaard Larsen, 21, told the Associated Press.

Swiss tourist Gerlinde Hoff, 60, stayed overnight at the airport with her husband and by midday was still waiting for another flight home, according to Reuters.

"They only say 'You have to wait, you have to wait, you have to wait," she said. "I'm angry and I'm tired. It was such a nice holiday and now it's a little bit not so nice".

Malaysia Airlines also said in a travel advisory on its website that it was avoiding airspace over Pakistan and northern India "until further notice''.

Pakistan aviation authorities said the country's air space would reopen as of midnight Thursday (2am on Friday in Thailand). The government closed it on Wednesday after Pakistan said its military had shot down two Indian warplanes and captured a pilot, escalating tensions between the nuclear-armed rivals.

India also suspended flights through some of its northern airports on Wednesday. Those facilities were back to normal on Thursday, but flights both to the US and Europe out of New Delhi were affected.

A United flight from Newark, New Jersey, to New Delhi was rerouted through London and later cancelled, and Air Canada cancelled flights from Toronto and Vancouver to the Indian capital.

Air China cancelled its flight on Thursday from Beijing to the Pakistani capital, Islamabad. According to an employee of the airline's publicity office in Beijing, the status of other flights would be decided later.

The closing of Pakistan's airspace saw Gulf Arab airlines, which serve as a link between East and West in global travel, rapidly reshuffle their flights.

In the United Arab Emirates and Bahrain, civil aviation authorities immediately halted their flights to Pakistan. Airlines in those countries include the long-haul carriers Etihad, Emirates and Gulf Air.

Saudi Arabian Airlines and Oman Air similarly cancelled flights to Pakistan. Pakistanis work in a variety of blue- and white-collar jobs across the Gulf Arab states.