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 under 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 urged people to move to emergency shelters and away from rivers, streams and ravines.
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, 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.
At least 27 people have been killed and four others were missing after the powerful Hurricane Otis slammed into Mexico's Pacific coast, officials have said.
Otis hit the beach resort city of Acapulco as a category 5 storm early on Wednesday and tore through the southern state of Guerrero, largely cutting off communications and road links with the region.
Photos of Acapulco show roads full of mud and debris and buildings that sustained heavy damage. More than 500 emergency shelters were opened for residents.
Thousands of Mexican military members have been sent to assist with clean-up operations.
"Unfortunately, we received word from the state and city governments that 27 people are dead and four are missing," Secretary of State for Security Rosa Icela told reporters on Thursday.
President Andres Manuel Lopez Obrador said that the deaths occurred around Acapulco, but provided few details. He acknowledged that the government was late in arriving because of the havoc Otis left behind.
Lopez Obrador, who made it into Acapulco late Wednesday, said the destruction was so complete in the impact zone that not a single power line pole remained standing.
"What Acapulco suffered was really disastrous," Lopez Obrador said.
At least 48 people died when Category 5 Hurricane Otis slammed into Mexico's southern Pacific Coast, most of them in Acapulco, Mexican authorities said Sunday as the death toll continued to climb and families buried loved ones.
Mexico's civil defense agency said in a statement that 43 of the dead were in the resort city of Acapulco and five in nearby Coyuca de Benitez. Guerrero state's governor had earlier raised the number of missing to 36 from 10 a day earlier. The death toll increased after authorities had raised it to 39 on Saturday.
In Acapulco, families held funerals on Sunday and continued the search for essentials while government workers and volunteers cleared streets clogged with muck and debris from the powerful storm.
A friend just told me about this tonight, that they didn't have a proper warning for how intense it was, It happened Tuesday and just today they got help. Sounded to me similar with the Hawaii situation. Funny it was hardly mentioned in the media at all.
Buffalo_Ken - it is getting more than difficult to not conclude definitively that weaponized weather is now a " tool " being deployed as part of the ambitions of the psycho elitist....coupled with Direct Energy Weapons and all around chaos for the masses....I hope folks are seriously prepared.
Comment: Update October 26
Al Jazeera reports: Update October 29
Associated Press reports :