An explosion has destroyed the 54-storey headquarters of oil giant Petroleos Mexicanos (Pemex) in Mexico City killing at least 25 people and injuring dozens of others.

The cause of the blast is yet to be ascertained while rescue workers are looking for more victims trapped under the rubble. The death toll is likely to rise sharply as local reports say more than 100 have been injured while another 100 could still be trapped in the collapsed building.

The explosion rocked the state-run oil giant a day after the company rolled out bold measures to buy new equipment. On the eve of the blast, Pemex director general Emilio Lozoya Austin had announced the company's latest expansion plans to buy more self-raising rigs.

Austin, who was on a business trip to Asia, has cut short his visit to rush back to the city.

Television images of the blast show massive damage to the building while the rescuers are seen carrying the victims in stretchers and office chairs.

"We have 13 dead at the scene and one more at the hospital. There are more than 80 wounded and we continue to look for survivors in the debris. Now we are in rescue mode and looking for people and for bodies," said Mexican Interior Minister Miguel Angel Osorio Chong earlier.

Sniffer dogs and rescue helicopters have also been employed to assist the officials in the operation.

One unconfirmed local report suggests that the blast was caused by a gas leak, while another indicates it was due to faulty machinery which exploded.

"The place shook, we lost power and suddenly there was debris everywhere. Colleagues were helping us out of the building," eyewitness Cristian Obele told Milenio Television.

Another witness named Maria Concepcion Andrade, 42, said: "We were talking and all of sudden we heard an explosion with white smoke and glass falling from the windows. People started running from the building covered in dust. A lot of pieces were flying."

The blast took place on the lower floors of the Pemex Executive Tower which houses several thousands of workers. Police have cordoned off the area, the commercial hub of the city.

Pemex, the world's fourth largest producer of crude oil, had earlier announced that the building had been evacuated due to a fear of electrical system failure.

The oil giant, a key contributor to Mexico's federal budget, has suffered a string of accidents at pipeline and refinery installations in recent years. However operations director Carlos Murrieta recently tweeted that the company had managed to reduce its accident rate.

An injured man is being transported in an office chair outside the headquarters of state oil giant Pemex in Mexico City - Reuters
Two women react while leaving the premises of state oil giant Pemex in Mexico CityReuters
An injured person is transported on a stretcher outside the headquarters of state oil giant Pemex in Mexico CityReuters
Ambulances and rescue personnel are seen on a street outside the headquarters of state oil giant Pemex in Mexico CityReuters
Police block a street leading to the headquarters of state oil giant Pemex in Mexico CityReuters
Shattered windows are seen on one side of the headquarters of state oil giant Pemex in Mexico CityReuters
Soldiers are seen on a street outside the headquarters of state oil giant Pemex in Mexico CityReuters
A man wheels an injured Pemex's employee as she leaves Pemex hospital in Azcapotzalco in Mexico CityReuters
Mexico's President Enrique Pena Nieto (L inside car) waves to the crowd while arriving at the headquarters of state oil giant Pemex in Mexico CityReuters
Relatives of Pemex's employees wait for information of their family members outside Pemex hospital in Azcapotzalco in Mexico CityReuters
Relatives of Pemex's employees wait for information of their family members outside Pemex hospital in Azcapotzalco in Mexico CityReuters
A man wheels an injured Pemex's employee as she leaves Pemex hospital in Azcapotzalco in Mexico CityReuters
Relatives of Pemex's employees wait for information of their family members outside Pemex hospital in Azcapotzalco in Mexico CityReuters