(Recasts, updates dead and recovered, adds detail)
By Odaliz Anaya
VILLAHERMOSA, Mexico, Oct 24 (Reuters) - A storm killed 18 Mexican oil workers fleeing a battered offshore rig, and Navy rescue teams were searching on Wednesday for seven people missing in the turbulent seas.
State-owned oil monopoly Pemex said 61 people had been rescued after huge waves knocked the Usumacinta drilling platform into an adjacent rig late on Tuesday.
Workers on the rig, in the Kab oil field in the southeastern Gulf of Mexico, had jumped into emergency rafts after the collision caused leaks in crude oil and natural gas pipes.
Exploration and Production Chief Carlos Morales called the accident one of the worst in Pemex’s history. The death toll could rise as bad weather hampered efforts by Navy rescue teams to locate other workers.
Attempts by rescue crews in eight helicopters and four rescue boats to reach life rafts were thwarted for hours by waves of up to 20 feet (6 meters).
The bad weather shut Mexico’s top three oil exporting ports in the crude-rich Gulf of Mexico for a second day, suspending oil shipments to the United States. Port officials saw it as unlikely they would reopen before Thursday.
Pemex said U.S. buyers of its oil should not be hurt as it would reschedule the delayed shipments once the storm passed.
It was not evacuating other oil platforms or shutting down production as the worst of the bad weather had passed.
The company said in a statement it would take up to five days to seal the leaking natural gas and oil but that the extent of the crude spill was less than previously thought.
Most of Mexico’s crude is shipped from the Gulf ports of Dos Bocas, Cayo Arcas and Coatzacoalcos, which were closed on Tuesday morning as a severe cold front brought stormy seas and high winds. Temperatures plunged as far away as Mexico City.
Some of the fleeing workers were believed to have fallen into the sea, drowning in the huge waves as 80 mph (130 kph) winds lashed the platform.
"The weather has not helped," Pemex chief executive Jesus Reyes Heroles told Mexican television. He said the damaged platform, 20 miles (32 km) from the port of Dos Bocas, was minor in terms of output.
Mexico is a top three supplier of oil to the United States, which takes around 80 percent of its southern neighbor’s oil exports. Ships stopped leaving port early on Tuesday and officials could not say when conditions would improve.
The Pacific coast port of Salina Cruz, from which Pemex ships roughly 300,000 barrels per day (bpd) of crude oil to the U.S. west coast and to Asia, was also closed on Wednesday due to high winds.
Pemex, which has exported an average of 1.708 million bpd this year, often has to deal with rerouting or rescheduling oil shipments to avoid storms and hurricanes on Mexico’s coast.
In August, Pemex evacuated 18,000 workers from its platforms and shut operations as Hurricane Dean rampaged through the Gulf of Mexico.
"For the moment, up until now, there is no impact on exports. Exports are not being affected," a Pemex official said, asking not to be named. "Even though exports are suspended, there is still time to reschedule the shipments." (Additional reporting by Cyntia Barrera Diaz, Jason Lange and Catherine Bremer)