Seven of the eight children said to have been left with potentially serious injuries following the collapse of an inflatable slide at Woking fireworks display have been discharged from hospital.

Emergency service said the other child was being kept in hospital for observations, but that their injuries were “not believed to be significant”.

Surrey Police declared a “major incident” after multiple children fell from the “giant inflatable slide” at about 7.30pm on Saturday.

The air ambulance helped transport one of the patients to “major trauma centres”, South East Coast Ambulance Service (Secamb) said.

One witness said he was concerned earlier that evening when he saw up to 40 children playing on the “flimsy” slide at once.

Andy Datson, 23, estimated the slide to be about 30ft 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 he noticed the flashing lights of ambulances after walking off with friends.

“I immediately thought that’s going to be the slide. 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 30ft tall.”

Oliver Trimble told the BBC that the evacuation was announced over the event’s loudspeakers shortly before 8pm, when the fireworks were due to begin.

A view of the scene at a fireworks funfair in Woking Park, Surrey (PA)

He said he saw victims being treated by medics, adding: “It was quite a horrendous sight to see.

“This is one of Woking’s biggest events of the year, thousands of people come to see the fireworks.”

Local musician Anna Neale said she was among the hundreds of people who left 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.

“I am very grateful my children didn’t go on it, let’s just put it that way,” she said.

Secamb had “multiple crews” at the scene of the “significant incident”. Police said the Health and Safety Executive had been informed.

Woking District Rotary Club, the event’s organisers, said it was “shocked and distressed” by the collapse.

The park will remain closed into Sunday as police investigate the cause of the incident, the club added.

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A Health and Safety Executive spokeswoman said “initial enquiries” were being made.

A Woking Borough Council spokesman said: “We will be working with the police and relevant authorities to understand and explain what happened.”

A statement issued by Surrey Police asked anyone who witnessed or had footage of the incident to contact officers.