A cliff fall behind a supermarket today just missed workers and shoppers and plunged the store into darkness.

Staff at Asda in Brighton Marina had to run for cover when rocks and debris fell into the yard.

They watched in horror as a water tanker, used to supply the store's sprinkler system, was bowled over and an electricity generator was knocked out by flying rocks.

More than 20 shoppers and 75 members of staff were evacuated from the area at about 8.30am and the store was closed.

Fire crews and police were on standby and a 300-metre area around the fall was cordoned off.

Asda personnel manager Darren Evans was working at the back of the store.

He said: "I looked behind me and saw it all come down. It hit the water tank, which went straight up in the air, before shunting a big freezer we keep at the back, and I just ran.

"I made sure everyone was OK and ran in the store and told everyone to get out.

"It was an incredible sight and was like something out of the film Vertical Limit."

Paul Medhurst, warehouse manager, said: "I heard a loud rumble, just like thunder, and a big bang.

"We have a freezer at the back and it was moving towards me and I just ran to the far end of the yard.

"It was so quick and I am very lucky. I've never heard anything like it. It was like an intense breaking of glass and I felt the earth shake."

Bryan Salvage, who works at Asda, said: "All the lights and the phone went down. There was a massive roar and the roof started shaking. People started to run out. No one knew what it was. We hit the alarm and everyone was out pretty quickly. Then I got outside and saw half the cliff had come down."

General store manager Jonathan Smith said: "It was the biggest cliff fall to date.

"There was a huge spillage of chalk into our back yard. We evacuated the building immediately and I'm pleased to say everyone is safe, although staff are shocked by the incident.

"We will be closed until we are told otherwise because we have no electricity and no sprinkler system. There is a large overhang of cliff and it is in a very dangerous position.

"We are very concerned about this. This is the biggest incident yet and we would like it sorted out."

Engineers from Brighton and Hove City Council arrived with workmen from power firm Seeboard.

On December 13, last year an estimated 800 tonnes of rock fell on to the undercliff walk on Brighton's eastern seafront.

Since then, there have been another 14 collapses after heavy rain.