Texas officials have announced that 12 bodies have been recovered from the site of Wednesday’s deadly blast at West Fertilizer plant.
About 200 people are now thought to have been injured in the blast.
Earlier, the town’s mayor said he believed four firefighters who attended the original fire were among the dead, though this has not been confirmed.
Dozens of buildings were destroyed by the blast in the town of West, near Waco.
Jason Reyes of the Texas Department of Public Safety said search and rescue efforts were ongoing.
The explosion produced a tremor similar to a small earthquake.
There is no indication that the blast and a fire which preceded it were anything other than industrial accidents, according to police.
However, they have said that the site is being treated as a crime scene.
Texas Governor Rick Perry earlier said he was declaring the area a disaster and would request an emergency declaration for federal aid from President Barack Obama, who has offered any help needed.
Air quality and gas pipelines are being monitored for safety, and gas supplies have also been disconnected until any risk has passed.
Emergency services officials earlier said the explosion may have been caused by the chemical ammonia.
The explosion devastated the West Fertilizer Company, about 20 miles north of Waco, in central Texas.
Dozens of homes were levelled and other buildings – including a school and nursing home a few hundred metres from the plant – were badly damaged.