Hurricane Otis has made landfall on the coast of southern Mexico, bringing wind speeds of up to 165mph (270km/h).
It touched down near the popular Acapulco resort just after midnight on Wednesday (06:25 GMT), the National Hurricane Center (NHC) said.
Authorities have warned of a life-threatening storm surge and the possibility of landslides as heavy rain pelts the area.
The storm has already begun to weaken as it moves inland.
David Hall arrived at the Princess Mundo Imperial resort in Acapulco for a work conference hours before Otis made landfall. He told the BBC that the building had been damaged by the wind and rain.
He said the hotel room windows buckled from the force of the winds and smashed, sucking items out of the room.
Mr Hall, who is from the Mexican city of Colima, roughly 600km (372 miles) from Acapulco, said the building “shivered” as if an earthquake was happening.
He and hundreds of other guests at the hotel have been hunkering down together while the worst of the hurricane passes.
“A lot of people are scared,” said Mr Hall.
A hurricane warning is in effect for a 350km-long stretch of coastline between the coastal towns of Zihuatanejo and Punta Maldonado in the state of Guerrero.
Power outages have already been reported in Guerrero, according to Mexico’s civil protection body. School classes across the state were cancelled in preparation for the storm’s arrival.
Unverified videos posted online show damage to a hospital in Acapulco and flooding outside the Copacabana hotel.
Mexico’s national water agency said that waves of up to 10 metres high (32ft) were expected on the coasts of Guerrero and in western Oaxaca state. Possible mudslides have also been forecast.
President Andres Manuel Lopez Obrador said there was “material damage and blocked roads” and that there were landslides on the highway to Acapulco.
He said there were no reports of deaths but cautioned that authorities were struggling to get updates.
“The hurricane is still affecting the area and communications are completely down,” he said.
Officials said that it was difficult to gauge the extent of the damage in Acapulco, which has a population of around 780,000, given poor communications.
The NHC also said that Otis was expected to produce up to 20in (51cm) of rainfall on Friday across Guerrero and western coastal areas of the neighbouring Oaxaca state.
Scientists said the speed with which Otis intensified from a tropical storm into a category five hurricane – the highest level of storm – on Tuesday was rare.
It broke the record for the fastest intensification rate over a 12-hour period in the Eastern Pacific, gaining 80mph in that time, according to meteorologist Philip Klotzbach.
Parts of Mexico’s Pacific coastline have already seen significant flooding earlier this month after Tropical Storm Max hit. Local media reported two deaths as a result of the storm in Guerrero.
A few days later, one man was reported killed after powerful Hurricane Lidia made landfall in the state of Nayarit, north-west of Guerrero.