The death toll from a Mexican gas plant fire rose to 29 while three workers remained missing Wednesday as witnesses recounted the terrifying blast and the inferno\'s intense heat. President Felipe Calderon ordered the prosecutor\'s office to investigate Tuesday\'s fire near the US border, which the state-run Pemex energy company described as an \"unusual accident.\" Two people who were reported missing turned up dead on Wednesday while another worker succumbed to his injuries, a Pemex spokeswoman told AFP. The company revised the number of injured to 26 and the missing to three. Hundreds of workers ran out of the plant after the explosion, and the ensuing fire\'s heat could be felt outside the facility, which houses huge cisterns, witnesses said. Blood was still visible at the entrance to the plant, which employed 700 people. \"It sounded like a bomb went off,\" the manager of a nearby gas station told AFP. \"There was an explosion and it kept thundering. We thought that everything was going to blow up.\" Quick-thinking by emergency workers prevented a bigger tragedy at the gas distribution center near the border city of Reynosa, Calderon said. \"Thanks to their timely intervention, (plant) workers, firefighters and the Mexican army were able to contain the fire relatively fast and avoid a real, major catastrophe,\" he said in Mexico City. The president said the government will take measures to ensure that homes, businesses and factories in the north continue to receive gas after the accident. The damaged plant receives natural gas from the Burgos basin and distributes the product to Pemex\'s gas and petrochemicals unit. \"We want to know exactly what happened, which is key to prevent this type of tragedy from happening again, particularly in such sensitive and strategic facilities for the country,\" Calderon said. Pemex has begun its own investigation into the accident, the third incident to hit a company facility since last month. Pemex pipelines have been targeted by fuel thieves in the past, causing leaks and in one case a deadly blast in 2010. \"We have no evidence that it was a deliberate incident, or some kind of attack,\" Pemex director Juan Jose Suarez, who toured the site, told reporters. \"All the evidence points to an unusual accident.\" On August 13, an explosion rocked a refinery in the northern city of Ciudad Madero, and on the same day a fire broke out at a pipeline in the central state of Hidalgo after thieves apparently tried to steal diesel from it. No injuries were reported in either incident. The previous worst incident took place in December 2010, when an oil pipeline exploded after it was punctured by thieves in the central town of San Martin Texmelucan, leaving 29 dead, injuring more than 50 and destroying 32 homes. In October 2007, 21 Pemex workers died during a gas leak on an oil platform in the Gulf of Mexico. Most drowned when they jumped into the sea in a panic. The latest incident gave another shock to the city of Reynosa, whose 600,000 residents already have to contend with armed drug gangs that regularly block roads during shootouts. Officials continued to search for the missing workers. Leslie Flores, a 22-year-old mother of a 10-month-old baby, was still waiting for news about her husband. Her brother-in-law was among the dead. An employee from Quimica Apolo, a Pemex contractor, had called her on Tuesday, warning her to brace herself because \"what awaited me was not good.\" She said authorities have asked relatives to provide DNA samples because \"some bodies were completely charred.\"