Mr. Obama's act authorizes the Department of Homeland Security and the Federal Emergency Management Agency to coordinate all disaster relief efforts for people suffering from the blast.
Flanked by local officials, Texas Gov. Rick Perry said during a news conference that all affected buildings had been cleared with possibly the exception of one burned home.
Before investigators confirmed the number of fatalities, the names of the deceased were becoming known in the town. A small group of firefighters and other first responders who likely rushed to the plant to battle the pre-explosion blaze was believed to among the dead. Authorities could not confirm how many of those killed were first responders.
The town's landscape has been forever changed by the four-to-five block radius leveled by the blast at West Fertilizer.
As search-and-rescue teams continue to pick through the rubble, some were allowed to go closer to the site of destruction and came back stunned. Emergency workers said it's possible that some residents would be let closer to their homes on Friday.
The blast registered as a 2.1-magnitude seismic event with the U.S. Geological Survey. But seismologists say their sensors can only record the ground motion, and that people who felt the shockwave above ground actually experienced a much larger event. Witnesses who were blocks away said they were thrown in the air by the explosion. Authorities say a large swath of the town looks like a bomb hit it.
Garage doors were ripped off homes. Fans hung askew from twisted porches. At West Intermediate School, which was close to the blast site, all of the building's windows were blown out, as well as the cafeteria.
The plant produces ammonium nitrate fertilizer -- the same chemical used in the Oklahoma City bombing. The company that runs the fertilizer plant was fined $10,000 last year for safety violations. The fine was reduced after the company took steps to improve safety at the plant.
Authorities believe that a fire at the plant may have caused the tanks to overheat, which sparked the explosion. There's no word yet on what caused the initial fire.
The Associated Press contributed to this report.