A section of Brighton’s seafront could be closed for weeks after the road collapsed into a pub in the historic arches below.

Structural engineers are working to assess the extent of the damage this weekend while a busy stretch of the A259 King’s Road eastbound remains closed off between West Street and Ship Street.

The collapse comes just months after it was revealed another section of structurally unsound arches along the seafront need tens of millions of pounds of work.

At 8am yesterday workmen trying to repair a leak at the back of the Fortune of War pub in the Kings Road Arches removed a piece of plywood on the arched roof.

Earthwork and rocks cascaded into the pub leaving a hole which revealing a disused water main and the tarmac of the road about 6ft above.

When the workmen realised there was no longer anything supporting the road they ran up and stopped the traffic on the A259, where the road had sunk.

Sussex Police cordoning off the scene from and surveyors from Brighton and Hove City Council and Southern Water assessed the damage.

Laurence Hill, manager of the Fortune of War, said: "We had builders working to shore up a fire exit at the back of the pub.

"They took out a part of ceiling and then loads of rubble just came down.

"It looks like there is nothing holding the road up at some points but luckily no one was hurt.”

At 11.30am yesterday morning the road was reopened east bound only for access and light vehicles, but the clogged up city remained congested throughout the day.

In a statement Sussex Police said: “Lorries and the majority of traffic are still being diverted via the B2185 Grand Avenue and The Drive, Hove, onto the A270 Old Shoreham Road.

“Westbound traffic is still being diverted north at the Aquarium roundabout/Palace Pier to follow the A23 London Road to join the A270 New England Road and Old Shoreham Road.”

Mr Hill said surveyors yesterday stripped away more of the panelling to check the integrity of the archway.

Mr Hill said: “I don’t know if there is a problem with the arch, but it looks like the builders came across some repair work done when there were still horse and carriages on the road, rather than heavy traffic.”

The pub reopened but its upper deck seating remained closed while the collapse was investigated.

A spokesman for Southern Water said: “Our engineers have been in Kings Road, Brighton, helping investigate the cause of the subsidence.

“This precautionary work included digging down to check our water mains.

“We have not found any problems with our mains that could have contributed to this issue.”

Brighton and Hove City Council executive director Geoff Raw said: “Structural engineers will be working over the weekend to assess the extent of the problem and which seems to have been caused by historic alterations to premises in the arches.

“We’re working as swiftly as possible with the police and key partners to ensure public safety and to keep the traffic moving as smoothly as possi ble.

“A contra flow system is now in place between Middle Street and West Street, please allow extra time for journeys through this area and check the council website for updates.”

In January this year The Argus revealed the city council faces a bill for almost £80 million of repair work on the seafront – including £65 million for the arches amid fears of possible collapse.

Mr Raw’s statement that yesterday’s collapse was caused by historic alterations to premises in the arches echoes the council’s statement in January, which said: “Many different forms of construction have been used over the last 125 years to build and then extend the arches.”

A council spokesman said the extent of any structural problem uncovered yesterday would not be determined until a survey was completed.

Yesterday opposition councillors called on Brighton and Hove City Council to take urgent action.

Councillor Warren Morgan, Leader of the Labour and Co-operative Group on Brighton and Hove City Council, said: “The collapse shows how critical the condition of our most important transport arteries is.

“It is vital for business, tourism and of course traffic and major disruption will do immense harm to our city’s economy.”

He said the council knows tens of millions of pounds needs to be invested in the city’s main seafront road and called for funding to be diverted from other projects.

Conservative group leader Geoffrey Theobald added: “I’m quite surprised that the situation has been allowed to occur.

“It’s a very important road and I’m just surprised it’s been allowed to happen. You assume engineers are constantly checking the road.”

In response Green Councillor Ian Davey, lead member for transport, said: “We recognised immediately that emergency action needed to be taken and working with the police and others, secured the area for urgent investigation.

“Strengthening the seafront is an enormous project which in total costs many millions more than the council has – especially after years of neglect.

“We have bid many times for government funding to help meet the bill, but unfortunately these weren’t successful.

“We are however spending an unprecedented amount of council money – over £2 million a year - on rebuilding sections of our seafront. This work is vital to our city and its economy.

“It’s disingenuous for Cllr Morgan to talk about diverting funds - he knows it’s not possible as that funding has been granted by the Local Enterprise Partnership to a specific project.

“It’s not ours to spend on anything else - and if we were to try, it could be taken away from the city altogether.

“Rather than playing political football and misleading residents about this serious matter, perhaps Cllr Morgan can support the council and police officers working hard to deal with this unforeseeable incident and get the city moving again as quickly as possible.”

Owners of businesses in other seafront arches were confident that the collapse was an isolated problem.

Mike Levy, owner of the Castor and Pollux art gallery, said: “This is not the Brighton seafront falling it is a localised incident – I am not concerned at all.”

Another business owner, who did not want to be named, said he believed if there was any real danger to their shops they would have been told to close.

Katty McMuarry, owner of Two Kats and a Cow, said: “I was concerned when I came down this morning and saw the road closed and the police around.

“The arches are old structures and we have assured by surveyors that they are structurally sound.

“We thought it was going to be a quiet day with all the rain and then this happened.”