Pheonix Natural Gas, which owns the main, sealed off the affected area around College Street.

The nearby Belfast Institute of Further and Higher Education had to be evacuated.

Traffic disruption

Phoenix Natural Gas chief executive Chris Murray, said that while the leak caused major traffic problems, the company's main concern was for public safety.

He said: ''Although it has been most unfortunate that there has been traffic disruption the primary consideration was to make sure that the area was safe in co-operation with the police and fire brigade.''

The leak started after a contractor hit a low pressure gas main at the junction of College Street and College Avenue in the city centre.

Mr Murray said: ''A DOE Water Service contractor hit a low pressure main at lunchtime.

'No risk'

''The area is now completely safe. We have checked the area and there is no risk whatever.

''One of the fortunate things with natural gas is that it is lighter than air and if we do get any damage to our system such as this it disappears off into the atmosphere.''

College Street between Queen Street and College Avenue is still sealed off as repairs continue.

The police are advising motorists to avoid the area.