An investigation will begin today into an explosion at a fireworks factory which killed two firefighters.

The firefighters died as they fought a blaze at the Festival Fireworks company’s storage depot near Lewes, East Sussex, yesterday.

The two officers were part of a team of emergency services workers. A further 12 people were injured in the blast, including nine members of the fire service, two members of the public and a police sergeant.

Eyewitnesses said the explosion rocked nearby properties and could be heard up to six miles away as debris was flung over a wide area.

Fireworks continued to explode amid a huge plume of black smoke from the burning properties several hours after the blaze first started.

Hospital bosses said two of those admitted had serious injuries and one was in intensive care. The others had more minor injuries.

One firefighter said more people could have died. "We were lucky it wasn’t 22," he said."

Investigators were at the scene of the fire on Sunday night which was to be left to burn because of acetylene gas canisters on the site.

The emergency services, community figures and members of fireworks company offered their condolences to the families of those that died.

Gary Walsh of the Fire Brigades Union (FBU) said one of the dead was a 49-year-old control room staff member who was also a retained fire officer.

The other was a 63-year-old retired fire officer who had been re-employed and provided support at incidents.

The union said they were the first firefighters to die on duty in England and Wales this year.

The news was broken to the families by East Sussex Chief Fire Officer Desmond Pritchard.

Lewes MP Norman Baker said: "It is a terrible event and I feel deeply sad for the families that have lost firefighters.

"It is always sad when someone dies, but particularly when they are serving other people and part of the emergency services and essentially putting their lives on the line for other people."

The drama began shortly before 2pm when members of the family-run Festival Fireworks company discovered a fire had broken out.

They fled the concrete and steel-reinforced buildings, on a remote industrial estate in Shortgate, between Lewes and Uckfield.

At first, 10 fire engines and crews were sent to the incident, but more officers were called in as the scale of the blaze became apparent.

The biggest explosion, at about 3pm, was followed by several smaller blasts as the fire spread to other storage buildings.

Residents compared the biggest explosion to a bomb. Jason Winter, nephew of owner Martin Winter, said his family had escaped without injury, but they had lost "everything".

He said: "They have literally got the shirt that they’re wearing at the moment, that’s it.

"They have lost everything, even down to their dog, their dog’s in the house, the dog has died.

"They have lost the house, they have lost garages, offices, all the buildings, they’ve lost their vehicles, their lorries, they have even lost their guinea pigs."

John Winter, the owner’s brother, said the fire could have been caused by an electrical fault.

He added that although Bonfire Night has recently passed, a substantial amount of fireworks remained at the property for Christmas and New Year celebrations.

The FBU’s general secretary Matt Wrack said most of the firefighters injured were retained firefighters. He said: "We extend our sympathies to the families, friends and colleagues of those who died.

"Death always touches everyone who works in the fire service. It may be old fashioned, but the Fire Service is like a family and deaths within the Fire Service are genuinely felt very deeply."

The Health and Safety Executive said an inspector was ready to start an investigation as soon possible to do so.

Noel Tobin, director of the National Campaign for Firework Safety, said: "This has been a very serious explosion and fire and calls into question the sort of fireworks we import from China into the UK."

Festival Fireworks employed up to 50 staff. As one of the biggest firework importers in the UK it was behind the Millennium display alongside the River Thames and the Lord Mayor’s show in London.