At least 30 people were trapped in the building after the blast, CNN affiliate Foro TV reported.
Citing local authorities, Foro TV said five people were killed, and 75 people were injured. CNN has not independently confirmed details about casualties from the explosion.
The blast prompted an evacuation of personnel from the Pemex offices, a company spokesman told Notimex.
A large plume of smoke rose near the office tower after the explosion.
Images from the scene showed emergency rescue teams carrying people on stretchers.
It was unclear how many people were injured or what caused the explosion, Pemex spokesman Francisco Montano told Notimex.
“There are injured and significant damage,” he said, according to Notimex.
CNN’s Rey Rodriguez and Rene Hernandez contributed to this report.
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