A concrete manhole cover was blasted into the air by an explosion, throwing clouds of dust and gravel towards shocked onlookers.

It was lifted from the pavement by an underground electrical blast as crowds of workers were leaving the American Express building in Edward Street, Brighton, shortly after 11.30am yesterday.

Witnesses heard the explosion before the 10kg cover landed back on the ground, leaving a hole in the road near the junction with Blaker Street.

Computer programmer Daniel Scrivener, 34, said: "I heard this bang and looked up to see the cover flying through the air.

"At first I thought something had fallen off the roof of a building and bounced off the pavement.

"There was a lot of dust everywhere and people came over to see what was happening.

"If someone had been walking across the manhole they would have been thrown up with quite a force.

"It was a real shock but fortunately no one was too near. If I'd been much closer it would have been dangerous."

Police and the fire brigade received several calls and officers guarded the gap in the pavement before EDF Energy workmen arrived to repair the fault and secure the manhole.

Electrical explosions can occur when underground cables are damaged or if water seeps into the wires.

An EDF Energy spokesman said: "We received a call from the fire brigade at 12.06pm after a fault on a piece of underground electrical equipment.

"Our engineers were on site promptly to investigate the fault and carry out repairs.

"Power supplies were not interrupted and we would like to apologise for the inconvenience caused."

In February, flames leapt more than 15ft from a manhole cover during an electrical fire which left dozens of homes in darkness.

The blaze started in an electrical box in a sewer at the junction of Surrey Street and North Gardens, Brighton, and engineers had to cut the supply to several homes.

In 1950, Kaarina Burgess was killed as she walked to work when she was hit by a piece of iron manhole cover in a gas main explosion in South Street, Worthing.