British Telecom was today unable to say whether it would take hours, days or weeks to restore the phone lines of 130,000 homes and businesses in Manchester destroyed by fire.

Intense heat has so far prevented telecom engineers from assessing the damage in the underground tunnel in Manchester where the blaze broke out at 3.20am.

Twelve hours after automatic detectors first alerted Greater Manchester county fire service to the fire in the tunnel, which lies buried 100ft below street level, BT workers had still not been able to gain access to the mile-long service tunnel.

The fire brigade announced at around 2pm that the blaze was out and the 7ft high tunnel was being ventilated to cool it down and clear the smoke. Fire investigation officers were waiting at the scene as well as telecoms repair staff.

Ross Cook, a spokesman for BT, said that the fire was "very serious".

"There are 44 cables in the tunnel, each containing 24 fibre optic cables, which together can carry an awful lot of traffic," said Mr Cook.

"That is why we bury them so far underground, to protect them from being accidentally cut by people working on the road. It is too early to say how long it will take to repair until the engineers can get in there and work out how much damage has been done."

Emergency services in Lancashire and Cheshire were working at full stretch to ensure that the 999 system was functional and to maintain communications with ambulances and other emergency vehicles.

In the worst case scenario, it would be a "big job" if if BT was forced to relay a full mile of fibre optic cable, Mr Cook said.

Meanwhile BT was trying to re-route calls wherever possible, with hospitals and emergency services as top priority.