Investigations were under way today into a gas explosion which left one man with severe burns and two other people injured.

The blast at the BOC Tradequip outlet in Whitby Road, St Anne's, left a man in his 50s with what paramedics described as "extensive" burns to his groin, arms and face. He was taken to the specialist burns unit at Frenchay Hospital.

The other two men, thought to the in their 40s or 50s, were taken to Bristol Royal Infirmary, one with minor burns to his neck and the other with concussion and hearing problems.

Police sealed off a large area around the site while firefighters worked to put out a blaze that followed the initial blast.

A 200-metre cordon around the site was set up by police because of fears of further explosions and led to the evacuation of the nearby Avon Meads shopping and leisure park, with businesses including the Showcase cinema forced to shut down.

Rail services were also affected, with services from Temple Meads station to Bath suspended and replaced by bus services. Other services were being diverted via Bristol Parkway because of the closure, which it is believed could be in place through much of today.

Avon Fire and Rescue Service has already started an investigation into the incident and Health and Safety Executive inspectors were also due to visit the site, on an industrial estate shared with more than half a dozen other companies, including a number of car dealers.

Emergency services were called to the BOC Tradequip base after two gas cylinders exploded at around 2.45pm yesterday.

Great Western Ambulance Service said the incident was believed to have happened as the man who suffered the most serious injuries was capping a canister of acetylene, a gas which burns at a high temperature and is commonly used in welding.

The service sent paramedics in rapid-response vehicles, ambulances and incident support officers to the scene. Whitby Road was sealed off at the roundabout exit opposite Sainsbury's and hundreds of cars were seen leaving the site following orders from police to evacuate.

Shoppers from the Avon Meads centre were also evacuated at 4.30pm, after officers extended the cordon around the scene for safety reasons.

Acting inspector Marc Milliner of Avon and Somerset police said: "Around 40 police officers were mobilised to deal with the situation. "On our arrival we initially set up a 150-metre cordon but extended that cordon further after discussions with the fire service. The cordon was set up for public safety because of concerns about possible further explosions."

Avon Fire and Rescue Service spokesman James Blaydon said: "A deluge system, which is in effect an industrial scale sprinkler system, operated to control the fire, which has now been contained.

"This is a multi-agency operation and is likely to operate for an extended period of time."

Witnesses working on the estate said they heard a loud noise just before 3pm.

Volkswagen dealer VW Heritage alone evacuated more than 40 members of staff from their branch in Pioneer Park.

Employee Justina Bior said: "We heard explosions twice, the roof of our building was shaking. I know two people have been hurt, hopefully they are alive. I was so scared."

Nick Gabriel, also of VW Heritage, said: "All I heard was this whooshing noise. We were not told what was going on, just to evacuate."

The safety cordon was expected to be in place until this morning at the earliest, with a possibility it could still be in place this afternoon.

Train services faced severe disruption after the section of the railway line that runs alongside the depot was closed. Six trains travelling from Bath Spa to Temple Meads at the time of the explosion had to wait several hours before being taken to Bath.

A shuttle bus service was set up to serve Bath Spa, Chippenham and Swindon, while services from Bristol Temple Meads to London Paddington were redirected from Temple Meads via Bristol Parkway.

Replacement bus services were also run from Keynsham and Oldfield Park, and a shuttle operated between Westbury and Swindon.

The incident was reported to the Health and Safety Executive as a matter of routine by police and inspectors are set to attend the scene in the next week to collect evidence and then determine whether a full investigation should be carried out.

Spokesman Wailim Wong said: "We will be looking into it, we will decide whether it merits an HSE investigation.

"In this case I understand it was related to explosives. We have a special team for explosives but they work on a national basis."

BOC – formerly known as the British Oxygen Company – supplies gases, chemicals and equipment to companies worldwide.

It is the second gas explosion at the same BOC outlet in the St Anne's area of Bristol in four years.

The previous incident was in May 2006, when two people were hospitalised after an explosion in part of the factory that works with dissolved acetylene.

A year earlier a 200-metre exclusion zone was set up when an acetylene cylinder overheated and firefighters had to be called in but there was no explosion in that incident.

In a statement following yesterday's incident BOC said: "BOC would like to express its concern for those who have been injured.

"Our emergency shutdown procedure was initiated and our deluge system activated to control the fire, which Avon Fire and Rescue Service have now confirmed has been contained. BOC very much regrets the inconvenience that has been caused to the local community."