Tropical Storm Marco prompts evacuation on oil platform

(Adds Pemex evacuation, storm location, platform details)

MEXICO CITY, Oct 6 (Reuters) - Tropical Storm Marco formed on Monday in the southern Gulf of Mexico, prompting Mexico's state-owned oil company Pemex to evacuate four offshore plants and shut down wells.

The 60 mile (100 km) diameter storm, which brewed up quickly on Monday, was 80 miles (129 km) northeast of Veracruz at 0000 GMT, the U.S. National Hurricane Center said.

Marco could possibly reach hurricane strength before making an expected landfall late on Monday or early Tuesday morning.

The Mexican government issued a hurricane watch for the country's eastern coast between Cabo Rojo and Veracruz.

Pemex said it was evacuating workers at its Lankahuasa, Bagre "B", Carpa "B", and Bagre "C" platforms.

The company also said it had shut six wells at Lankahuasa, which primarily produces natural gas, and was taking preventive action at onshore oil facilities along the Gulf coast.

Despite the storm, Mexico's government reported that all three main oil exporting ports on the Gulf of Mexico were open as of Monday afternoon.

Mexico reduced oil production by 250,000 barrels per day on Sept. 24 due to refinery outages in the United States caused by Hurricane Ike. Weather-related disruptions to shipping have prevented Pemex from boosting output since then. (Reporting by Robert Campbell, Cyntia Barrera Diaz, editing by Alan Elsner)