Only hours after technicians had diverted some Warrnambool services through the South Melbourne exchange, a fibre optic cable was accidentally cut at Meredith about 3pm today.

Technicians from Geelong and Ballarat have been dispatched and Telstra hopes to have the problem resolved by midnight.

Customers affected are at Macarthur, Port Fairy, Casterton, Wandovale and Timboon.

EARLIER: IT could have been Telstra's worst nightmare when the fire alarm went off this afternoon at the Warrnambool central exchange.

A fire brigade crew with sirens wailing raced to the Koroit Street building, reminiscent of early morning on November 22 when flames disabled the vital regional communications control centre.

However, the early-afternoon incident turned out to be just a case of a leaking toilet tripping the alarm system.

Water cascaded onto the alarm panel, triggering an alert to the fire station five blocks away.

"It's not the situation we really needed just a day after restoring services," Telstra spokesman James Howe told The Standard.

"But we can assure people there was no damage at all to our equipment.

"Crews are continuing with their work of fixing customer faults.