Three people suffered serious burns in a major fire at a waste management plant in West Lancashire.
Up to 60 firefighters were called to reports of an explosion at PHS waste management in Tollgate Road, Burscough, at about 1000 BST.
A 52-year-old man was airlifted to the Royal Preston Hospital and two others were taken to Whiston Hospital.
They are being treated for burns to their faces and hands. The fire is now out and crews are damping down.
An investigation is under way into the cause of the fire.
It is not yet clear what kind of chemicals were involved in the explosion but gas tests on the smoke found it was low toxicity.
At the fire's height, plumes of thick black smoke were billowing from the building and could be seen six miles (9.7km) away.
'Like an earthquake'
Police cordoned off the estate and advised people to avoid the area and close their windows and doors.
Philip Hattersley, who works nearby, said: "There was a really loud bang and then everything just shook - it was like an earthquake really.
"I went outside and there were really big mounds of smoke just coming out of the building which is about 100yds away."
Other eyewitnesses described the noise like "popping fireworks" with visible high flames and smoke with an acrid smell.
Barry Graham, from Lancashire Fire and Rescue Service, said crews had managed to stop the fire spreading to two adjacent buildings.
He said specialist teams had been brought in to assess the scene and its safety for those fighting the blaze.
A PHS spokeswoman said: "Lancashire Fire and Rescue has confirmed the fire has been put out and the clean-up operation is now underway.
"All other operations on site have been shut down and safely isolated.
"A full internal investigation will be launched shortly and we are committed to cooperating with any external investigations to establish how this incident occurred so that it does not happen again."