Emergency crews have been put on 24-hour alert across Limerick and Clare as the River Shannon threatened to inundate towns and villages.

Officials said areas in south east Clare were most at risk after energy chiefs moved to ease water levels upstream on Lough Derg.

Localised flooding was already reported and authorities warned the damage was expected to spread as volumes allowed through the Parteen Weir increase.

"Areas of south east Clare, particularly those located along the lower River Shannon, are priority areas and are the focus of ongoing attention," a spokesman said.

Councils warned Montpellier, Castleconnell, O'Briensbridge, Clonlara, Westbury and Shannon Banks were expected to bear the brunt.

Limerick city was expected to escape the deluge as water levels remained about two feet below the critical level.

Council staff, fire and rescue units, the ESB, Army, health workers, gardai and the Civil Defence were called in across the lower Shannon area on 24-hour stand-by.

Some 4,000 sandbags have been delivered to the affected areas.

"Arrangements are in hand to evacuate a small number of affected families in the Hampstead Park, Shannon Banks area and accommodation will be arranged where necessary for those people," a spokesman said.

"We have been informed by the ESB that exceptional flooding exists along the River Shannon - the highest on record and this requires the ESB to increase the amount of water that must be released at Parteen Weir. The discharge levels have been growing in recent days but the release of higher volumes of water downstream was unavoidable."