Fire officials fear that the number of casualties could rise much higher -- as many as 60 to 70 dead, CNN reported citing George Smith, the emergency management system director of the city.
The blast took place at the West Fertilizer Plant, about 18 miles north of Waco, about 8.50 p.m. Wednesday. It sent a massive fireball into the sky. Flames leaped over the roof of a structure and a plume of smoke rose high into the air.
"There are lots of houses that are levelled within a two-block radius," Smith was quoted as saying. "A lot of other homes are damaged as well outside that radius."
ABC News, citing Texas Department of Public Safety spokesman Gail Scarborough, put the number of injured at 200; 40 of them are critical.
Besides the injuries, 75 to 100 houses and business were completely destroyed in and around the plant, Scarborough was quoted as saying.
CNN said residents are being evacuated because officials are worried that another tank at the facility might explode.
Shortly after the explosion, more than 60 patients streamed into Hillcrest Hospital in Waco, suffering from "blast injuries, orthopaedic injuries (and) a lot of lacerations", said hospital CEO Glenn Robinson.
While some of the injuries are minor, others are "quite serious", he said.
At least six helicopters are going to fly out those who are injured, Robinson said. Others are being transported by ambulance, and some are getting to the hospital by car, he added.
Two other hospitals in the region were also assisting.
The West Fertilizer Plant is just north of Waco. A school and a nursing home are among the buildings near the plant, CNN affiliate KWTX reported.
Chrystal Anthony, a nearby resident, said she saw the flames engulf the nursing home and an apartment complex.
"It was an apartment complex that was devastated, the nursing home. The fire was close to a residential area," Anthony was quoted as saying.
"It was like a bomb went off," said Barry Murry, a resident who lives about a mile away from the plant. "There were emergency vehicles everywhere. It has been overwhelming."