Teenagers are flinging themselves into the sea from the top of the helter-skelter on Brighton's Palace Pier in a deadly new summer craze.

Managers have called the police as youths clamber over roofs and canopies to leap more than 50ft into the waves.

Police say they are powerless to act but, as thousands headed for the beach today, safety officials said the daredevil fad could kill.

Coastguards who make annual warnings against jumping from sea walls and groynes at the shore end of the pier were horrified at the latest twist on the dangerous game.

A spokeswoman said more thrill-seekers were making the leap this summer and were taking extra risks.

She said: "We've become increasingly alarmed at the dangerous lengths these people are going to in order to pursue this insane activity.

"Not only are jumpers running along the roofs of the pier buildings and canopy covers but two people have been spotted jumping from the helter-skelter.

"The vast majority are teenagers or young adults and we're concerned their daredevil antics will end in tragedy. They are foolishly and needlessly putting themselves at risk."

A Coastguard spokesman said: "It's a crazy thing to do. It's dangerous because it's hard to judge the tides and to know how deep the water is, especially from the height of the helter-skelter.

"We've dealt with people who will spend the rest of their lives in a wheelchair after diving into shallow water.

"Go to the beach and have fun but don't put yourself in any danger, even if it seems like a good idea."

A worker at Brighton and Hove City Council's seafront office said: "Jumping into the sea from the pier is not the recommended thing to do as there are rocks beneath the surface.

"But jumping from the helter-skelter is just insane."

A pier spokeswoman said: "Brighton Pier would like to appeal to not only the teenagers but also their parents to call a halt to this activity before anyone gets injured."

Bookmakers Ladbrokes today closed all bets on the mercury hitting 37.7C (100F).

But at noon the Met Office was predicting Sussex's top temperature would not exceed the 36C (96.8F) forecast for Gatwick this afternoon.

By 11am this morning, thermometers in the Hove garden of Ken Wodhams, The Argus' weatherman, suggested the heat would remain bearable today, with the temperature reaching 23.3C (74F). A sea mist is keeping temperatures low.

Sussex Ambulance Service took 648 calls yesterday on one of its busiest days of the year.

But as thousands flocked to the coast, the county's transport continued to buckle.

Trains on all South Central routes were limited to 60mph and delays were expected throughout the day.

The AA warned motorists that Tarmac could melt and advised them to ensure radiators were topped up to prevent engines overheating.