A serious disruption to the phone network in Dublin left thousands of users in the south and centre of the city without a service for long periods yesterday afternoon.

Land-lines were affected when software crashed in an exchange in Stillorgan, Co Dublin, and Eircell mobile phones went down when an exchange at Hely House, Dame Court, was flooded with water.

Land-lines were out of action for about 3 1/2 hours, while mobile phone users were still experiencing problems last night.

Mobiles in the Dublin 1, 2, 3 and 4 areas will not be back to normal until this morning, said an Eircom spokesman, because of the flooding.

The first problem occurred when software in an Eircom exchange at Priory Park, Stillorgan, crashed and calls could not be processed. The problem was exacerbated when back-up software also failed.

The collapse of the Priory Park exchange caused a domino effect on exchanges in the centre of Dublin and businesses were left without a service from about 2.30 p.m to 6 p.m.

Some 80,000 land-lines were effected initially, but this rose significantly as other exchanges were hit. People making calls to numbers in the affected areas were unable to reach them.

The spokesman said the company "sincerely apologies for the disruption caused and we realise the serious impact it has on our customers".

He added that the problems were "seriously regrettable" but would not be repeated and had no connection with the Y2K problem.

A statement from Esat Digifone said there were no problems with its network, but the breakdown in Eircom's network had created congestion because some customers made "extra call attempts" and this led to difficulties in connecting some calls.

The Eircom spokesman said when software in the Priory Park exchange crashed all the calls were diverted to the Merrion exchange which serves the city centre, but this also crashed.

The company which supplied the software, Ericsson, sent a team of technicians to assist Eircom staff in repairing the faults.