Some 200 other people were injured in Wednesday's blast in West, a small town of 2,800 people located 80 miles (129 kilometers) south of Dallas, Texas Department of Public Safety spokesman Jason Reyes told a news conference.
Investigators are treating the blast site as a crime scene, although authorities say the blast was likely caused by a fire at the West Fertilizer Company.
Fifty homes were destroyed, while teams have searched 150 homes and have another 25 to go.
"We are still in a search and rescue mode," Reyes said, after giving the death toll.
Until now, officials had refused to release a firm toll, saying only that it was between five and 15.
Speaking at the same press conference, US Senator John Cornyn said that 60 people were still unaccounted for in the "terrible tragedy."
Texas governor Rick Perry however later said that that figure was expected to drop as residents rushed to hospitals or staying with friends and relatives are accounted for.
The blast came with the entire country already on edge after the attacks on the Boston Marathon that left three dead and more than 180 wounded on Monday.
In Washington, President Barack Obama told the Texas blast victims that they were not forgotten, despite the national focus on Boston.
"We've also seen a tight-knit community in Texas devastated by a terrible explosion," Obama said in a televised statement after the second suspect in the marathon bombings was captured in a suburb of Boston.
"I want them to know that they are not forgotten. Our thoughts, our prayers are with the people of West, Texas, where so many good people lost their lives, some lost their homes, many are injured, many still missing."
Obama signed an emergency declaration for Texas late Friday allowing federal funds to help in the rebuilding effort.
One of those killed was a Mexican national, Mexico's foreign ministry said late Friday.
The victim was 57 years old and lived in apartments located in front of the plant, a foreign ministry official told AFP, speaking on condition of anonymity. The official did not identify the victim, but said that he was a native of the northern state of Zacatecas.
In West, which was largely deserted Friday, a pharmacist who lived near the fertilizer plant told AFP his home had sustained major damage in the blast.
"I saw the house, it's in bad shape. The door is blown in, windows are blown in. All of the ceiling has collapsed onto the floor. I think that the roof is still intact but it was dark and I didn't get a real good look," said Michael Sulak, a lifelong resident of West.
Patrick Swanton, a local police sergeant, said the search was "very slow, methodical, tedious.
"They are having to do a lot of shoring up of homes to be able to make sure they are safe to get into," he added.
"They will take the necessary time to investigate this thoroughly to determine what happened and make sure that if in fact there was any criminal wrongdoing, that they find that and be able to figure that out."
The West Fertilizer Company was fined by US regulators in 2012 over its transport of hazardous materials, documents showed.
Last year, the company was fined $10,100 by the US Pipelines and Hazardous Materials Safety Administration for mislabeled cargo tanks and "failing to develop and adhere to a security plan" for transporting a large quantity of anhydrous ammonia, according to a copy of the citation.
The company reached a settlement with US regulators in which it paid a $5,250 fine.
The violations concerned the transport of anhydrous ammonia -- which lacks water -- and not its storage at the factory itself, which exploded nearly an hour after a fire broke out Wednesday evening, according to local officials.
"We are hoping for the best but we are preparing for the worst," said Swanton.