Powerful serial blasts shook the factory of pharmaceutical major Ranbaxy in Mohali on Wednesday night setting off a major fire that left at least 20 people injured.

At least 40 technical personnel were on duty when the blasts took place at the production centre of the factory followed by the fire, Senior Superintendent of Police G P S Bhullar said.

He said people from nearby houses were being evacuated due to toxic fumes generated by burning chemicals.

Bhullar said out of the 20 people injured, two had 100 per cent burn injuries.

He ruled out sabotage and termed the blasts as 'purely accidental'.

The first explosion rocked the factory at around 2235 hours and was followed by a series of low-intensity blasts, Bhullar said.

Twenty-fire tenders From Ludhiana, Ropar, Chandigarh and other nearby areas were pressed into service and the blaze was put out shortly before midnight.

The injured were admitted to different hospitals and the police cordoned off the factory premises.

Bhullar said preliminary investigations showed the blast had taken place in a generator set inside the factory's production centre.