Hurricane Patricia strengthened into a potentially catastrophic Category 5 storm as it churned toward Mexico's Pacific coast, having grown at an "incredible rate" in the past 12 hours, the World Meteorological Organization said on Friday.

"Patricia is now the strongest ever hurricane to hit the eastern north Pacific region," WMO spokeswoman Clare Nullis told a U.N. briefing in Geneva, citing an update from the U.S. National Hurricane Center (NHC).

"This is really, really, really strong. It's comparable with Typhoon Haiyan which hit the Philippines with such devastating affect a couple of years ago."

Haiyan killed more than 6,300 people and wiped out or damaged practically everything in its path as it swept ashore on Nov. 8, 2013, destroying around 90 percent of the city of Tacloban in Leyte province.

Patricia, which became a hurricane overnight, had maximum sustained winds of about 185 miles per hour (295 km per hour) as it moved toward the north-northwest at 10 mph (16 kph).

"The winds are enough to get a plane in the air and keep it flying," Nullis said.

Patricia was last located about 185 miles (295 km) south-southwest of the port of Manzanillo, where a hurricane warning had been issued. A hurricane warning was also in effect for the beach resort of Puerto Vallarta.

The storm, which is a "Category 5", the highest rating possible, had been expected to weaken somewhat before making landfall in the hurricane warning area by Friday afternoon or evening, the Miami-based hurricane center said earlier.

The United States government issued an advisory urging its nationals to steer clear of beaches and rough seas and to take shelter as instructed by Mexican officials.

Some businesses in Puerto Vallarta had begun boarding and taping up windows late on Thursday as a precaution, while several domestic flights had been delayed.

Mexican emergency officials began to prepare shelters and warned people in the states of Colima, Jalisco and Michoacan to get ready for torrential rainfalls.

None of the major installations of Mexican state oil giant Pemex lie in the projected path of the storm. 

Reuters (Reporting by David Alire Garcia, additional reporting by Tom Miles in Geneva; Editing byAngus MacSwan)