At least eight children are being treated for "potentially serious injuries" after an inflatable slide collapsed at a fireworks funfair in the UK, police have said.

The incident happened in Woking, Surrey, a town to the south-west of London.

Surrey Police declared a "major incident" at Woking Fireworks after multiple children fell from the "giant inflatable slide" at about 7.30pm on Saturday evening.

Local police said that Woking Park was evacuated as medics, including an air ambulance crew, treated the children this evening.

One witness said he had been concerned earlier that night when he saw up to 40 children playing on the "flimsy" slide at once.

South East Coast Ambulance Service said it had "multiple crews" at the scene of the "significant incident".

"Our clinicians have treated six children on scene for potentially serious injuries," Seacamb said in a statement.

The patients were being transported to "major trauma centres" in London with the help of the air ambulance, the statement added.

Andy Datson, 23, said he saw up to 40 children playing on slide, which he estimated was about 30-foot tall at its highest.

"We had been walking past the slide earlier in the night and said it looked unsafe. It looked pretty flimsy to say the least," he said.

"There were far too many kids on it.

"It didn't look like it could hold that many people."

The journalist, who lives in Guildford, Surrey, said that he noticed the flashing lights of ambulances after walking off with friends.

"I immediately thought that's going to be the slide," he said.

"It looked like there were too many children on it and the side area had given way," he said.

"If, heaven forbid, they fell from the top I would say it's at least 25 to 30-ft tall."

Local musician Anna Neale said she was among the hundreds of people who evacuated the park, which had been packed with families with young children.

The 36-year-old said: "We saw all the blue lights and saw the air ambulance arriving. We all evacuated very calmly. Everyone was just shocked."

She had planned to take her daughters, aged 10 and six, on the giant slide after the fireworks.

Woking District Rotary Club, the event's organisers, said it was "shocked and distressed" by the collapse.

"We are focusing in assisting the emergency services in dealing with the injured children," a statement added.

"Our thoughts are with the children and their families at the moment.

The fireworks "extravaganza" had been due to start at 8pm.