BT engineers on Tuesday were still working to repair 130,000 business and consumer phone lines, and disrupted data services, 36 hours after a fire hit a critical cable tunnel in Manchester.

The fire service is investigating an electrical fault as the possible cause of the blaze, which took cables down at 2 a.m. on Monday morning, a BT spokesman told Techworld. But the company could not give an estimated time for when all customers would have services restored.

The disruption has affected business phone lines, corporate Web sites, call centres and residences, with banks, Internet hosting companies, power companies and airlines among those reportedly hit. BT said it was re-routing traffic around the area but that the impact from the loss of the circuits had spread as far as South Wales.

"Engineers only got access to the tunnel at nine or 10 o'clock last night because it was pretty dangerous in the tunnel," the spokesman said. "They have been working through the night and today to set up their equipment and to join up cables."

He said that engineers were setting up alternative ducts between the two buildings connected by the tunnel, which is 30 metres below street level. Damaged fibre was being replaced and new cables were being installed to bypass burnt ones. BT could not say how many of the 130,000 customers in the central city location were businesses.

The Co-operative Bank, based in Manchester, was one major company hit by the outage. The bank said that one of its call centres, in Portland Street, could no longer make outgoing calls. The bank was forced to fall back on its disaster recovery plan and relocate 80 staff to another office in the city.

A spokeswoman said that customers phoning the centre had their calls automatically re-routed to the switchboard at the second building. Workers' shifts also had to be managed to fit around those of the staff already using the second building. "It takes a certain amount of management and planning - the key is forward planning, absolutely," the spokeswoman added.

Powergen's website was unavailable as of Tuesday afternoon, displaying a message attributing the outage to the tunnel fire. The telephone lines of Manchester Internet Exchange, a Web hosting company, appeared to be down.

The mile-long Manchester tunnel connects two major exchanges and carries 44 cables, each carrying 24 optical fibres.