There were reports that some injured people had been taken to hospital. The airport was closed until further notice, and departing passengers were put up at local hotels.

Police said two people had been arrested following the incident.

Sky News later reported that a Scottish hospital where one of the arrested car bomb suspects was being treated had also been evacuated.

In the United States, which is gearing up for July 4 Independence Day celebrations, senior officials called the Glasgow incident a 'terrorist attack', and the White House raised security levels at airports.

Witnesses told the BBC that the vehicle - a Land Rover or a Jeep Cherokee - had exploded shortly after crashing into the glass front doors of the terminal. They said there had been a heavy stench of petrol.

'The car came speeding past at about 50 kph. It was approaching the building quickly,' witness Scott Leeson said. 'Then the driver swerved the car around so he could ram straight in to the door. He must have been trying to smash straight through.'

Taxi driver Ian Crosby, who was waiting outside Glasgow's Terminal One, said: 'A stocky Asian man had got out of the car and was quickly tackled to the ground by angry bystanders.'

A separate witness told Sky News that a man attempted to take a gas cylinder from the car before it went up in flames, but that could not be independently confirmed.

Mr Stephen Clarkson, a witness, told the BBC that one of the men in the car went up in flames as well.

'His whole body was on fire,' Mr Clarkson said. 'Immediately after the airport official put him out with the extinguisher, he got up off the ground. He did not seem like he was distressed.'

Police attempted to restrain the man, 'but the guy was quite strong and started fighting with the police', Mr Clarkson told the BBC.

Another witness told Sky News that the men in the vehicle were wearing boiler suits.

Glasgow Airport, Scotland's largest, handles around 8.5 million passengers a year and would have been packed with holidaymakers at the time of the incident, which took place at around 3.15pm local time (10.15pm Singapore time), police said.

It was unclear immediately whether the Glasgow and London incidents were connected but experts said the timing and the fact that all involved car bombs suggested that they were.

'One has to conclude...these are linked,' Dame Pauline Neville-Jones, former head of Britain's joint intelligence committee, told Sky News television. 'This is a very young government, and we may yet see further attacks.'

Reuters, AP, AFP

Hunt on for London car bomb trio