MEXICO CITY (CNN) -- An explosion rocked the offices of Mexico's state oil company Thursday, killing at least 14 people and injuring dozens more, officials said.
At least 100 people were wounded in the Mexico City blast, Interior Minister Miguel Angel Osorio Chong told Foro TV.
Dozens of people were trapped in the building after the explosion, Foro TV reported. More than five hours after the blast, rescuers had pulled at least one survivor from the rubble, Mexico's president said in a Twitter post.
And crews were still searching Thursday night for people who could be trapped in the Pemex office complex, which includes one of the city's tallest skyscrapers.
The explosion occurred in a basement and collapsed two floors of a building adjacent to the well-known tower, said Carlos Javier Rodriguez Jurado, one of the first paramedics to arrive at the scene.
"We found many people trapped" after the explosion tore through the building "from the inside out," he said. Six hours after the explosion, Rodriguez said people were likely still stuck in the rubble.
It was unclear what caused the blast, and Mexico's attorney general's office is investigating, Pemex said in a statement. A large plume of smoke rose near the building after the explosion around 4:00 Thursday afternoon, and emergency crews swarmed the scene.
"People were screaming. ... You could see pieces of the wall falling to the ground," said Joaquin Borrell Valenzuela, an attorney for the Pemex comptroller's office, who was in a courtyard outside the building at the time of the blast.
Outside the building, frantic family members searched for loved ones, and shaken witnesses described the explosion.
Mario Guzman said he was on the 10th floor of the tower when he felt "a very strong blow."
"We felt like the whole building was going to collapse," he told CNNMexico.
Images from the scene showed emergency rescue teams carrying people on stretchers. Authorities said helicopters carried some of the wounded to hospitals.
Mexican President Enrique Pena Nieto surveyed the damage Thursday night, along with Osorio Chong and Mexico City's mayor.
The Pemex headquarters includes a 54-story building that is nearly 700 feet tall, was built in 1979 and withstood the 8.1 magnitude earthquake that shook Mexico City in 1985, according to Emporis, a company that tracks building data worldwide.
The explosion occurred in an annex building just to the east of the tower, Foreign Minister Jose Antonio Meade said.
Officials evacuated the complex and operations will cease there until further notice, the company said.
The state oil company's director, who was on a business trip in South Korea this week, said in a Twitter post that he would return to Mexico immediately.
"We will get to the bottom of the causes in close coordination with the authorities," Pemex Director General Emilio Lozoya Austin said. "At this time, attending to the injured is the priority."