Pemex Chief Executive Luis Ramirez said on the weekend that safety was the company's "number one priority" following a rash of environmental accidents in recent months, including an ammonia leak in Veracruz state in April that killed six people.

A local official said on Thursday he saw a column of oil some 15 metres (49 feet) high spurting out of a ruptured pipeline in Tamaulipas, spraying black gunk over nearby fields. There were no casualties.

"It was as high as a tree. We estimate about 150,000 liters (950 barrels) of oil were spilled," Juan Flores, civil protection chief in the municipality of Altamira, told Reuters.

"This is the first time we've had an accident of this size here, but no property or people were affected," he added.

He said repairmen worked all night to fix the pipeline which by Thursday afternoon was operating normally, running to a nearby refinery. A clean-up operation was still under way.

The day before, a combined oil and gas pipeline exploded in the oil-rich southeastern state of Tabasco, polluting some six hectares (15 acres) of land, according to environmental watchdog Profepa.

"It's almost getting to be a daily thing," a Profepa spokeswoman said.

Pemex recently appointed a special working group to try and beef up safety standards after a rash of pipeline leaks, most of them in the Gulf of Mexico state of Veracruz.

Yet the company, which has limited funds after paying 61 percent of its revenues in tax, says it needs billions of dollars to repair 22,961 miles (33,738 km) of aging pipelines.