Erick made landfall as a Category 3 hurricane near the resort town Puerto Escondido in Oaxaca around 5:30 am local time.
Buildings and boats were damaged, and leaving areas strewn with debris, and streets were flooded.
By mid-afternoon, it had slowed to a tropical storm as it moved inland, with sustained winds weakening to 85 kph.
In coastal towns, residents began clearing the damage. "There are many boats sunk here," said fisherman Eduardo Gonzalez in Puerto Escondido. "We're here to help our colleagues."
Officials cautioned that Erick's intense rains remained dangerous.
"Life-threatening flooding and mudslides are expected, especially in areas of steep terrain," the US National Hurricane Centre said, forecasting up to 20 cm of rain for Guerrero state with around 10 cm for its neighbouring Oaxaca and Michoacan states.
Mexico's environment ministry also warned of waves of up to 10 metres.
No deaths were immediately reported, Laura Velazquez, the head of Mexico's civil protection agency, said at a press conference.
Two hospitals had suffered damage and power supply was compromised, she added. State-owned utility CFE reported that more than 123,000 users had lost power in Oaxaca, with service restored to 26 per cent by late morning.
Oaxaca Governor Salomon Jara said roads and highways were significantly damaged.
Erick is the earliest major hurricane to make landfall in the eastern Pacific, meteorologists from AccuWeather said.
"Rapid intensification near coastal cities is a major concern this hurricane season...as water temperatures continue to increase," said Alex DaSilva, AccuWeather lead hurricane expert.
Areas around Acapulco are especially vulnerable, AccuWeather said, as the beach town is still recovering from the impact of Hurricane Otis which hit in 2023.
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