By David Agren and Michael Winter
MEXICO CITY - An explosion rocked the headquarters of Mexico's state-run oil monopoly Pemex, killing 25 people, injuring 101, and damaging three floors of Mexico's second tallest building before sending plumes of smoke into the Mexico City skyline.
The blast ripped through the lower level of a building adjacent to the Pemex tower in central Mexico City at about 3:45 p.m. local time (4:45 p.m. ET) Thursday, forcing the evacuation of 3,500 employees, company officials said.
The cause of the blast has not been confirmed. Local media reported that machinery exploded in the basement of an administrative center next to the Pemex tower in Mexico City, which has more than 50 floors.
The Mexico City government sent rescue teams with search dogs to look for victims buried in the basement of a building known as B2. Government spokesman Eduardo Sánchez said rescue workers were trying to reach approximately 30 people still trapped inside the office complex. At least one person was pulled alive from the debris late Thursday, the Interior Ministry said.
President Enrique Peña Nieto said via Twitter that searching for survivors and attending to the injured were the top priorities. He tweeted that he would go to the Pemex site to personally oversee rescue operations.
"I deeply regret the deaths of Pemex workers and colleagues. My condolences to the families," Peña Nieto said via Twitter.
"We're going to get to the bottom of this, to carry out these investigations to, first, know what really happened, and if someone is responsible in this case, apply the full weight of the law," Peña Nieto told the El Universal newspaper.
Before the blast, Pemex - Petróleos Mexicanos - announced it had evacuated the tower as a precaution because of electrical problems.
The El Universal newspaper reported that an overheated air conditioning unit may have caused the blast. Another outlet reported it may have resulted by a buildup of natural gas.
No suggestions of sabotage or terrorism have been made, although some of the president's most persistent critics floated conspiracy theories.
The Associated Press reported that the blast blew out windows on three floors of the auxiliary building.
"Glass flew in all directions, parts of objects that I don't know where they came from. All the car alarms went off; I froze," Pemex worker Indira Rojas told the newspaperReforma.
One worker on the 10th floor described to NPR "an amazing explosion" and being thrown from his chair.
McClatchy Newspapers' Mexico City correspondent wrote that the blast hit at "the end of the Mexican lunch break when hundreds of people would have been moving about the complex."
After the explosion, outpourings of condolences from the country's political class poured in, a reflection of Pemex's importance to the country.
Pemex produces petroleum that provides approximately one-third of federal revenues, but the company has been plagued by operational difficulties.
A September accident at a Pemex gas processing plant near the U.S. border at McAllen, Texas, claimed 26 lives, while the theft of combustibles from its pipelines is rife - and often blamed on organized criminal groups. Investigations into such incidents are often unsatisfactory, says Houston-based energy analyst George Baker.
"Accidents come and go, but knowledge of the causes will not become public information," says Baker, publisher of Energia.com.
Mexico produces 2.5 million barrels of oil daily, a figure in decline due to overproduction and a lack of new reserves.
The Mexican oil industry was nationalized in 1938 and only Pemex may commercialize the country's reserves.
Peña Nieto has pledged to open Mexico's oil industry to outside investment, while keeping Pemex in government hands.