14 killed in blast at offices of Mexican state oil company

NEW: Mexico's president tours the scene of the explosion 14 people were killed and at least 100 are injured, interior minister says Rescuers are searching for people trapped in the building Witness: "People were screaming. ... You could see pieces of the wall falling"

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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 injured in the Mexico City blast, Interior Minister Miguel Angel Osorio Chong told Foro TV.

Dozens of people were trapped in the building after the blast, Foro TV reported.

Osorio Chong said rescuers were searching for survivors in the Pemex office complex, which includes one of the city's tallest skyscrapers.

The explosion occurred in the basement of a building adjacent to the well-known tower, officials said.

It was unclear what caused the blast, and Mexico's attorney general's office is investigating, the state-run Notimex news agency reported.

A large plume of smoke rose near the building after the explosion around 4 p.m. Thursday, 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.

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, Notimex said.

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."