Scores of people were forced to evacuate David Lloyd Ipswich in Ransomes Europark when a fire broke out.
One witness said up to 250 people fled the leisure complex after around 20 liquid petroleum gas cylinders “exploded” in an outside storage area near the main entrance.
Clouds of black smoke were seen billowing from the site while it was evacuated.
Around 15 firefighters arrived shortly after 4.20pm and the blaze was soon put out and brought under control, said group commander Dave Pederson, of the Suffolk Fire and Rescue Service.
He said an investigation to establish the cause of the fire has not yet taken place, but said it is not currently being treated as suspicious.
David Lloyd Leisure is expected to remain closed tonight. It is set to re-open tomorrow morning.
Bare-footed swimmers in just their shorts were among dozens of people seen running back into the leisure centre to collect their personal items when it was declared safe to return before leaving.
It is understood at least one nearby business provided shelter to club members and staff.
David Warren, 53, of Ipswich, said he was on a treadmill when he heard the fire alarm go off.
He said: “Between 200 and 250 people must have evacuated. We were told to leave and it was done safely. We waited around 20 minutes to get back in.”
Another witness at the scene said: “Some people said they heard an explosion.”
On the Ipswich Star’s Facebook page, Danny Brown wrote: “The staff there did a fantastic job, making sure everyone was safe and warm (bearing in mind some of us had to be evacuated in just our swimwear).
“They brought out towels for everyone, making sure the kids were ok and not panicked. Very professional. Nobody was ever in any danger.”
Mr Pederson added: “The fire involved 20 variously-sized liquid petroleum gas cylinders in an external storage container in a storage yard.
“It was difficult to access the fire (because) the cylinders were exploding when we arrived. We had to fight the fire initially behind protection.
“(But) the fire was brought under control within five minutes.
“All members of the public were evacuated by staff members, who did very well and did everything right. It was a safe evacuation and all the procedures were put in place.
“We don’t know what caused the fire, but will investigate when it is safe to do so. There are no suspicious circumstances at this stage.”
In a statement, a spokesman for David Lloyd Leisure said: “We can confirm that David Lloyd Ipswich was evacuated and closed due to a fire in a storage yard next to the main building on Tuesday, October 21, at approximately 4.15pm.
“Damage was mainly limited to the storage yard area and there were no injuries.
“At David Lloyd Leisure, we do our utmost to ensure the safety of our members and team members.
“Our team members undertake comprehensive training to ensure that when these rare incidents do occur, they are fully prepared and trained to deal with them as they were on this occasion.
“The club is due to re-open tomorrow morning after having being thoroughly checked and given clearance by the emergency services.
“The cause of the fire is currently being investigated. We apologise for any inconvenience to our members as a result of this temporary closure.”
Firefighters are expected to remain at the scene tonight to keep a watching brief.
Were you inside the leisure complex when it was evacuated? Please comment below.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here