A hurricane that swept into Mexico as the most powerful storm ever recorded in the Western Hemisphere rapidly lost energy on Saturday as it moved inland, but it left a path of destruction in its wake and sent thousands of people scrambling for shelter.

As nervous residents and frazzled tourists awoke to flooded roads and widespread power failures, rescue workers were sent up and down the western coast to assess the damage.

President Enrique Peña Nieto said there were no initial reports of deaths but warned that the storm continued to pose a threat. “We still can’t lower our guard,” he told the nation late Friday night.

As the hurricane continued to move inland it was downgraded to a tropical storm. But the authorities warned that heavy rains could still cause flash flooding and landslides.

“Many hillsides can weaken and collapse with Hurricane Patricia’s rain. Watch out!” warned Mexico’s civil protection agency.

The eye of the storm, Hurricane Patricia, made landfall Friday at around 6:15 p.m. local time near Cuixmala in Jalisco State, in southwest Mexico. While powerful, the storm was compact, with the highest winds felt only about 35 miles from its center.

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As it slammed into the coast, the storm was still firmly within the Category 5 range, with winds topping 165 m.p.h., strong enough to lift cars from the street, tear the roofs off house and pull trees up from their roots. But it quickly lost force, slowing to about 130 m.p.h. before 10 p.m.

By 1 a.m. Saturday it had been downgraded to a Category 2 storm, with winds of about 100 m.p.h., and by early Saturday morning it was downgraded further, to a tropical storm, with winds below 50 m.p.h.

One local resident, Jesús Alejandro del Angel Ruiz, 22, took advantage of a lull in the wind and rain Friday night to step out of his home in the Tapeixtles section of Manzanillo and survey the damage. He found fallen trees, branches, light poles – and two of his neighbors’ roofs.

“This area we live in gets flooded and that’s what this hurricane left: floods,” Mr. del Angel said. “A few zinc roofs went flying. The storm lifted them off, even though they had been secured. The storm had the strength to just lift them. “

He said a Category 1 storm that hit the area in 2011 left much heavier damage. It appears that improvements to drainage canals after that storm and the government’s efforts to evacuate vulnerable areas this time paid off, he said.

Although Mr. del Angel’s neighborhood was flooded, several other areas that are usually swamped during storms were dry on Friday night.

“There were moments last night that the winds were a bit strong and the sound it made was really ugly,” Mr. del Angel, a communications student, said Saturday. “It was surprising that nothing more happened.”

The governor of Jalisco, Aristóteles Sandoval, speaking at a news conference from Puerto Vallarta, said that there was no “irreparable” damage but that there had been “severe infrastructure damages.”

The roads were blocked in many areas by downed trees and other debris, making it hard to assess the damage.

“We still need to be alert,” he told reporters.

Hurricanes often begin losing strength once they hit land, since they lose contact with the warm ocean waters that give them energy, and Hurricane Patricia was no exception.

The National Hurricane Center warned, however, that “strong and damaging winds at higher elevations could persist through this morning,” and that heavy rain “is likely to cause life-threatening flash floods and mudslides in the Mexican states of Nayarit, Jalisco, Colima, Michoacan and Guerrero through today.”

The National Weather Service office in Brownsville, Tex., issued flood warnings for South Texas communities likely to be hit by heavy rains through Sunday.

In North Texas, near Corsicana, a 64-car Union Pacific freight train derailed overnight after heavy flooding washed away a section of the track. No one was hurt, but two crew members were forced to seek safety when a section of the derailed train became submerged in the rising waters, the local authorities said.

As the outer wall of the hurricane swept over the coast in Friday afternoon, trees were quickly flattened, landslides tumbled along a major road, light poles were toppled and roofs flew off.

“You had to feel how the air trembled,” said Yael Barragan, a trucking service coordinator in the port city of Manzanillo, huddled in his home with five children and four other adults. When the wind started blowing, it was not long before a neighbor’s roof was in his backyard. “I saw it fly, and I saw it land in my patio,” he said.

Margarito Figueroa, a construction worker in Naranjo, just north of Manzanillo, which was hit by the full force of the storm, said as the wind tore through the town Friday night he expected to find more extensive damage on Saturday morning.