MANZANILLO, Mexico (AP) — Hurricane Patricia headed toward southwestern Mexico Friday as a monster Category 5 storm, the strongest ever in the Western Hemisphere that forecasters said could make a "potentially catastrophic landfall" later in the day.

Residents of a stretch of Mexico's Pacific Coast dotted with resorts and fishing villages on Thursday boarded up homes and bought supplies ahead of Patricia's arrival.

With maximum sustained winds near 200 mph (325 kph), Patricia is the strongest storm ever recorded in the eastern Pacific or in the Atlantic, said Dave Roberts, a hurricane specialist at the U.S. National Hurricane Center.

Patricia's power was comparable to that of Typhoon Haiyan, which left more than 7,300 dead or missing in the Philippines two years ago, according to the U.N.'s World Meteorological Organization.

Hurricane Patricia became the strongest storm ever measured on the planet early Friday, with experts warning it could trigger 40-foot waves along southwestern Mexico and “life-threatening” flash flooding.

More than 7 million residents — and an estimated tens of thousands of U.S. citizens visiting or living there — were told to prepare for the “worst-case scenario” as the ferocious storm was expected to race ashore on Mexico’s Pacific coast between 6 to 10 p.m. ET Friday.

The tourist magnets of Puerto Vallarta and Manzanillo were directly in the Category 5 storm’s projected path, and Puerto Vallarta’s airport was closed Friday out of precaution as some stranded vacationers described their inability to fly out a “nightmare.”