More than 130,000 internet users remain offline this morning following yesterday's underground fire.

The blaze destroyed fibre cables linking BT customers to the internet. Both ADSL and dial-up users have been affected.

BT engineers were allowed to access the tunnel, 30 metres below the streets of Manchester, at 9-00pm on Monday night. It is unclear how long customers will have to wait because engineers are still assessing the scale of the damage.

BT said teams had worked through the night getting equipment into the tunnel. "Conditions are pretty grim down there and we have had to set up power, lighting and ventilation systems first. We cannot say at this stage how long the whole process will take because of the difficult conditions in the tunnel," said a representative.

"As cables are brought back into service, service to customers will be gradually restored. Additionally we have set up alternative ducts between the two buildings involved and will be putting in new fibre cable during the course of the day."

No decision has yet been made on whether customers will receive compensation for the outage. BT's representative said the first job was to concentrate on getting vital 999 services back online. The company said those in the Greater Manchester area should use mobile phones if they needed to contact the emergency services.

Greater Manchester County Fire Service officers have yet to establish the cause of the blaze but first signs indicate that electrical equipment in the tunnel may have been responsible.