A strictly Orthodox boy was believed to have drowned while swimming in a pond on Wednesday.

Thought to be in his mid-to-late teens, the Charedi boy had been swimming at Hampstead Heath in north London during the spell of hot weather.

Eyewitnesses said he had been playing in shallow water in an area not designated for swimming, and was seen calling for help before disappearing under the water.

Emergency teams rushed to the scene, but were unable to locate his body. Helicopters were also used in the search.

Witness Miriam Orlander said: “Someone told the family off for swimming where they shouldn’t. It was right at the other end from where the lifeguard would have been, so by the time he was struggling, it would’ve already been too late.

“One woman said she heard the boys shouting for help, but only realised afterwards because at the time she couldn’t understand what they were saying. The emergency services arrived very quickly, but you can’t make miracles. It’s just a tragedy.”

Six fire crews with around 30 firefighters were called. Local station manager Sam Kazmanli, who was at the scene, said: “Firefighters used three boats on the pond and carried out a methodical search.

“Despite our best efforts we were unable to locate the man and have handed the incident over to the police.”

A London Ambulance Service spokeswoman said that paramedics and a specialist response team had been sent to the scene and arrived within eight minutes.

“Despite the crews’ best efforts, the patient was not found,” she said.

The incident happened at around 5.30pm, with the rescue efforts stopped two hours later.