It had strengthened into a Category 2 hurricane after reaching Category 1 last night NZT.
Forecasters warned of intense rainfall across the Mexican states of Oaxaca and Guerrero, bringing “life-threatening flooding and mudslides”.
Mexican authorities said they were also expecting heavy rain in Chiapas state.
President Claudia Sheinbaum urged people to avoid going out and advised those living in low-lying areas or near rivers to move to shelters.
In Acapulco, a major port and resort famous for its nightlife, police with bullhorns walked along the beach and drove around town warning residents and holidaymakers of the storm’s arrival.
Some shops boarded up their windows and operators of tourist boats brought their vessels ashore.
Laura Velazquez, national co-ordinator of civil protection, said the Government was using the preventive patrols and social media to warn people.
Around 2000 temporary shelters have been set up in Chiapas, Guerrero and Oaxaca, and hundreds of troops and electricity workers have been deployed to help in any clean-up effort.
Local authorities have suspended classes and closed ports along the coast, including the port of Acapulco, to shipping.
Mexico sees major storms every year, usually between May and November, on both its Pacific and Atlantic coasts.
In October 2023, Acapulco was pummelled by Hurricane Otis, a powerful Category 5 storm that killed at least 50 people.
John, a Category 3 storm that hit last September, caused about 15 deaths.
-Agence France-Presse