Hurricane Otis strengthened on Wednesday to a Category 5 storm as it made landfall in Mexico, where it's likely to bring "catastrophic damage," the U.S. National Hurricane Center said.

The hurricane, which had been a tropical storm as of Tuesday morning, rapidly intensified within 24 hours.

Wind speeds approached 165 mph on Wednesday as the storm approached Acapulco, a Mexican resort town, at about 1 a.m. local time, according to a bulletin.

Flash flooding is also possible with up to 20 inches of rain are expected through Thursday in areas including Guerrero and the western coastal sections of Oaxaca, officials said.

"This rainfall will produce flash and urban flooding, along with mudslides in areas of higher terrain," the National Hurricane Center said.

The storm was expected to remain at Category 5 hurricane through landfall before weakening as it moves over "the higher terrain of Mexico," the center said.

"Otis will likely dissipate over southern Mexico on Wednesday night," the bulletin said.