Almost 40 people were treated by paramedics following a chemical leak at a Haven holiday park swimming pool.
Emergency services, including police, fire crews and an air ambulence, were called to Wild Duck Holiday Park in Belton near Great Yarmouth in Norfolk at about 2.30pm yesterday afternoon.
Police said the entertainment complex was evacuated but the pool was declared safe at about 5.30pm.
Norfolk Fire Service said vehicles including an environmental protection unit dealt with a chlorine leak.
An East of England Ambulance Service spokeswoman said swimmers had been treated for breathing and asthma problems. Eight were taken to hospital in a stable condition.
Haven Holidays spokesman, Tom Cassidy, said about 40 people were treated with 33 of them taken to hospital as a “precaution”.
He told the BBC: “There was a chemical leak in the indoor swimming pool in the entertainment complex and it was evacuated while police and fire and rescue were on their way.
“The casualties have been described to me as walking wounded.”