UPDATE: The official deaths are 33, but will keep rising.
The "official" number. Of course the deaths are over 25 and rising. RIP all the victims.
BBC News.- At least 14 people have died and another 100 were injured in Mexico City after an explosion at the headquarters of Mexico's state oil company, Pemex.
Emergency services, assisted by dogs, are searching for people trapped in the rubble. The cause of the blast is under investigation, Pemex says.
The 54-floor Pemex Executive Tower houses hundreds of employees.
Last September, 30 people died in an explosion at a Pemex gas plant in northern Mexico.
At least 13 people were killed at the scene while another person died later in hospital, Mexican Interior Minister Miguel Angel Osorio Chong told reporters.
A further 100 people were injured in the explosion. It is not clear how many individuals remain trapped beneath the rubble. Some reports have placed the figure at more than 30.
Television pictures showed debris from the blast spread out on to the street in front of the building, and Red Cross ambulances on the scene attending to the injured, our correspondent in Mexico City reports. Police have cordoned off the streets around the building, which is located in a busy commercial area of Mexico City.
Pemex said on Thursday evening it was investigating the possible causes.
The firm's chief executive, Emilio Lozoya Austin cut short a business trip to Asia and was on his way back to Mexico, the company added.
Relatives of employees have gathered outside the building in search of information about their loved ones, local media report.
Some are said to have tried to reach employees on their mobile phones but had no reply.
"The place shook, we lost power and suddenly there was debris everywhere. Colleagues were helping us out of the building," eyewitness Cristian Obele said.
"We were talking and all of sudden we heard an explosion with white smoke and glass falling from the windows," another witness said.
"People started running from the building covered in dust. A lot of pieces were flying."
Images of the blast posted on Twitter revealed large clouds of smoke billowing from the building. TV footage showed people being transported from the scene by helicopters. President Enrique Pena Nieto and Mexico City Mayor Miguel Angel Mancera headed to the scene of the blast. Mr Nieto said Pemex rescue and security teams were working alongside city authorities to help the injured.
"I am deeply sorry for the deaths of our fellow workers at Pemex. My condolences to their relatives," Mr Nieto said on Twitter.
"At the moment, the priority is to help the injured and protect the physical safety of those who work there."
The president said he has ordered an investigation into the causes of the blast. Earlier on Thursday, Pemex had reported problems with the electricity in the building in a message on Twitter. It later confirmed that an explosion had taken place "in the B2 building of the administrative center".
"There are injuries and damage on the ground floor and mezzanine," it said.
Plaster had fallen from the ceiling of the basement and the situation was "delicate", a spokesman for local emergency services was quoted by the Reuters news agency as saying.
Pemex has experienced a number of fatal accidents in recent years.
Last September's deadly blast at a gas plant near the northern town of Reynosa is thought to have been caused by a build-up of gas.