Hurricane Max made landfall in Mexico on Thursday, whipping its Pacific coast with winds of 130 kilometers (80 miles) per hour, the Miami-based National Hurricane Center said.
The Category One storm barreled into southwestern Guerrero state and is expected to pour heavy rain on neighboring Oaxaca, still suffering the effects of a massive earthquake last week.
Max has triggered warnings of life-threatening conditions in areas hit by the devastating 8.2 quake, which killed 96 people.
Guerrero state and western parts of Oaxaca state were forecast to receive 12.5 to 25 centimeters (five to 10 inches) of rain, with some areas receiving more than 50 centimeters.
The US National Hurricane Center warned rainfall could cause "life-threatening flash floods and mudslides" in the region, where some 12,000 homes had been damaged by the quake.
"Preparations to protect life and property should be rushed to completion," the NHC had warned earlier Thursday.
Local authorities have opened shelters to the population and shut down schools across the state.
Communities along a 300-mile stretch of coastline from Zihuatanejo to Punta Maldonado braced as Max strengthened from a tropical storm to hurricane force in the early hours of Thursday as it surged towards the Mexico.
Directly in its path is the tourist city of Acapulco, where persistent rain and strong winds kept vacationers away from beaches in advance of the hurricane, according to local television reports.
Fishermen and leisure boaters in Acapulco had heeded the weather warnings and taken their boats up as the storm closed in on the coast.
Mexico's National Electricity Company said it had deployed teams near the areas in the path of the hurricane in order to be able to restore power quickly in case of cuts.
According the center, Max was moving at 13 kilometers an hour and was expected to weaken to a tropical storm within hours and dissipate over southern Mexico Friday.
Oaxaca is still struggling to recover after it bore the brunt of the damage from a 8.2 magnitude earthquake that struck Mexico only last Thursday, leaving 96 people dead.
Oaxaca governor Alejandro Murat said on Monday that aid distribution following last week's quake was complicated because of the mountainous terrain.
Max was expected to bring dangerous storm surge that will likely cause "significant" coastal flooding, accompanied by "large and destructive waves."
Meanwhile, Mexico's National Water Commission said late Wednesday that heavy rain is expected in Michoacan and Colima states on the Pacific coast
The NHC said another tropical storm, Norma, had formed in the Pacific and was currently around 580 kilometers south of Cabo San Lucas in northwest Mexico.
Last week Hurricane Katia battered the Atlantic coast of Mexico and later blew itself out in the center of the country without causing major damage.
At the beginning of September, Tropical Storm Lidia left six people dead on its stormy passage through the state of Baja California Sur, in Mexico's northwest.
Mexico is one of the countries most vulnerable to hurricanes because of its thousands of miles of coastline on both the Atlantic and Pacific and its proximity to the hurricane belt.