An investigation has been launched into a huge blaze at an industrial farm building in Eccleston.
Police and fire officers are working together in the aftermath of the fire on Towngate.
Earlier residents were urged to stay indoors as thick black smoke covered the town.
The blaze is now under control.
A Lancashire Fire and Rescue spokesman said fire crews were likely to remain at the scene for some time damping down any hotspots.
Police diverted traffic away from the area and urged local residents to stay inside and shut their windows at the height of the blaze.
It is understood gas cylinders were exploding inside the building
One local , who asked not to be named, said: "There was a huge explosion and flames.
"Smoke was everywhere.
"Police told us to go back inside and shut the windows because the smoke was toxic so we did.
"There were lots of smaller explosions as well."
Watch manager Mark Woodward of Penwortham fire station praised the work of his colleagues.
He tweeted: "First in attendance with @Leyland_Fire at this incident.
"Excellent early action to prevent injury and fire spread to neighbouring properties,"
It was not clear to whom the commercial unit belongs
Another local resident said: "I couldn't believe the amount of smoke coming from the area.
"Suddenly there were fire engines everywhere."
Stewart Newman said on Facebook: "Could see the smoke from St Annes."
It is not believed that anyone has been hurt.
There has been no comment yet from Lancashire Constabulary.