A view of Petare neighbourhood in Caracas. AFP

The tanks were holding diluent, which is mixed with extra-heavy Orinoco belt heavy crude to make it lighter, legislator Jose Brito said in a telephone interview.

"These two tanks were holding diluent," Brito said. "Fortunately there were no injuries."

An oil industry source who asked not to be identified said the two tanks were located at a pumping station associated with the Petro San Felix project.

Venezuela's heavy crude upgrading projects turn tar-like Orinoco crude into more valuable grades of oil. Moving the heavy crude from production fields requires mixing it with some form of diluent that allows it to flow through pipelines.

State oil company PDVSA typically uses either light crude or fuel as diluent.

It was not immediately evident what the tanks were holding.

PDVSA did not immediately respond to a request for comment.

Photos on social media that users said were from the project, in the state of Anzoategui, showed flames coming out of two structures with large black plumes of smoke rising in the air.

Reuters