The main A27 east of Chichester was sealed off today as the desperate battle to prevent the city centre from flooding was intensified.

Drivers were urged to avoid the city as the Westhampnett bypass was closed for 24 hours.

A massive operation with pipeline running across one of the busiest roads in West Sussex was launched last night as water continued to cascade from saturated downland into the badly swollen River Lavant.

Dozens of firefighters and Environment Agency workers are also laying a pipeline beneath the road which is not due to reopen until 2am on Saturday.

The closure brought new traffic chaos to a wide area of the county with the B2166 between Bognor and Chichester already shut because of flood prevention work. It meant the only route into Chichester was A259 through Bognor which has already been choked with traffic all week.

West Sussex County Council information chief, Jane Robinson, said today: "We are urging people not to attempt to get to Chichester from the east unless their journey is really urgent.

"There was no alternative to closing the road. The work is absolutely critical because of the sheer volume of water that has to be pumped away.

Today's scheduled meeting of the full county council at Chichester was cancelled because most councillors have to travel to County Hall along the bypass.

The city's High School for Girls and Boys together with the giant Bishop Luffa Church of England Comprehensive School were all shut for the day.

In the city centre a massive pumping operation was stepped up yesterday as the latest threat to the city started to develop.

Pumps which had been switched off were reactivated as rain water began swelling the Lavant to levels higher than in 1994, when part of the centre of Chichester suffered major flooding, causing millions of pounds in damage.

Thousands of extra sandbags were brought in and fire crews spent most of the day checking and shoring up riverside walls which were in danger of collapsing.