Eight fire engines remained today at the scene of a large blaze on an industrial estate.
More than 100 firefighters were called to the blaze at the Lancashire Enterprise Business Park in Leyland at about 5pm yesterday, which destroyed up to five buildings.
People living near the site in Centurion Way were warned to stay indoors because of smoke, surrounding roads were closed, and parts of the West Coast Main Line were shut.
Crews arrived to find a "well-developed" fire in a building storing toilet paper, which spread to a neighbouring building containing chemicals, Lancashire Fire and Rescue Service said.
Firemen determined early on there were no people trapped in buildings, but 20 homes were evacuated after the chemicals became engulfed by fire.
A technical support team later deemed the chemicals not to be harmful, but local residents were advised to remain indoors and keep windows shut because of smoke.
Police put a cordon in place and urged motorists to avoid the area yesterday.
A Lancashire Police spokesman said there were no reports of injuries, adding: "We would like to reassure people that at this time there is nothing to suggest anybody is any danger."
Local reports suggested explosions could be heard coming from the blaze, with a large fiery glow cast over the site.
The blaze was brought under control just before midnight, but a spokesman said eight appliances remained on the site damping down the flames.
Paul Richardson, of the fire service, said it was unlikely the fire would be out completely for "two to three days at least".
A spokesman added: "The main West Coast railway line remains shut at this time as smoke continues to blow across the tracks and because of beer barrels exploding in the close vicinity.
"A number of roads are also closed in the area and they will remain shut until it is safe for them to reopen."
At the height of the incident, Lancashire Fire and Rescue Service had more than 100 firefighters at the scene, along with 20 fire engines, two aerial ladder platforms, a high volume pump and a mobile fire station.
A joint investigation by police and fire crews to find out the cause of the blaze will be held once the fire is completely out and the scene is declared safe.