Rescuers have carried out a painstaking search for survivors of the fertiliser factory explosion.
Authorities said they feared they would find more bodies in the rubble of homes and businesses levelled by the blast.
Texas Governor Rick Perry described the explosion as "truly a nightmare scenario" as he announced he was seeking a federal disaster declaration that would make more money available.
Police Sergeant Patrick Swanton from Waco said the tragedy killed "anywhere from five to 15" people, but warned he expected that toll to rise as local hospitals treated more than 160 people with varying injuries.
Swanton said officials were conducting a door-to-door search and rescue operation "to find survivors, to find people that are injured".
The blast, felt up to 80km away, destroyed an apartment complex and nursing home.
Yesterday, President Barack Obama offered the prayers of the nation to the people of West, a town of about 2800 people.
"A tight-knit community has been shaken, and good, hard-working people have lost their lives," he said, offering the assistance of the Federal Emergency Management Agency.