The blaze was reported from Bharat Petroleum's refinery in Chembur area.
"After a preliminary treatment at Bharat Petroleum's first aid centre, 22 were allowed to go home and 21 were shifted to Inlaks Hospital in Chembur. They have fractures and lacerated wounds," deputy commissioner of police Shahji Umap told the media.
The condition of one injured is said to be serious, he added.
According to fire officials, the blaze broke out at around 3:30 p.m. local time following several explosions. "Some 10 fire tenders have been pressed into service," a fire official said.
"Due to the tremendous heat and build up pressure, firefighting is being carried out from a safe distance using fixed monitors," chief fire officer P.S. Rahangdale told the media.
"The fire is on, but under control," the oil company has said in a statement.
A probe has been ordered into the incident, another police official said.