The explosion occurred in one of the units used to make high-grade fuels but BP was unable to confirm the cause of the blast.
According to news reports at least fifteen people had died.
The blast was felt miles away and broke the windows of many houses in the area. Thick, black plumes of smoke followed the flames and billowed over the area. Several cars and trucks parked on the site exploded in the extreme heat.
Television reports showed workers carrying out the injured on stretchers and officials at local hospitals said at least 20 people were being treated for injuries and that some appeared to be in critical condition, according to a Reuters report.
Non-essential personnel were evacuated from the refinery but other parts of the plant continued to operate, an AFP report said.
The 1,200-acre complex produces 30% of BP's North American oil supply and three per cent of the entire US supply. According to BP, the Texas City site groups 30 refinery units and handles 460 million barrels of oil a day. It pumps out enough gasoline to fill up a car every seven seconds.
News of the refinery explosion sent gasoline futures prices on the New York Mercantile Exchange to all-time peaks over $1.60 a gallon in electronic trade and psuhed up cash prices in the Gulf Coast region.
On March 30 last year, a large explosion and fire occurred in a gasoline-making unit but there were no injuries. The 2004 blast resulted in citations for 14 alleged violations from the Occupational Safety and Health Administration.