Hurricane Willa has swept onto Mexico’s Pacific mainland with 120mph (195km/h) winds, hitting beach towns, fishing villages and farms after roaring over an offshore penal colony.

The US National Hurricane Center said the category 3 storm hit near Isla del Bosque in Sinaloa state on Tuesday night, and federal officials said there were early reports of power blackouts and damage to tin-roofed structures.

Damage assessments were limited by darkness and disrupted communications, and no extensive information was expected until first light on Wednesday.

Forecasters said the hurricane could bring six to 12 inches (15 to 30cm) of rain – with up to 18in (45cm) in some places – to parts of Jalisco, Nayarit and Sinaloa states, with flash flooding and landslides possible in mountainous areas.

The storm’s forward movement sped up to 17mph (28 km/h) but began to lose its potency as it swirled over high ground. The hurricane center said Willa was expected to rapidly weaken overnight.

Willa came ashore about 50 miles (80km) south-east of Mazatlan, a resort city that is home to high-rise hotels and about 500,000 people, including many US and Canadian expatriates.

Although hotels, restaurants and stores were boarded over, people ventured onto Mazatlan’s coastal boulevard to watch a spectacular sunset as the hurricane obscured the sky to the south.

Alberto Hernandez, a hotel worker in the town of Teacapan close to where the storm made landfall,said he and his son, who also works at the hotel, were staying on the job, though the rest of his family had left the area.

Workers board up windows before the landfall of Hurricane Willa, in Mazatlan, Mexico, on Tuesday. Photograph: Marco Ugarte/AP

“We’ve had rain all day. There is nobody in the streets. Everything is closed,” Hernandez said. “But not everyone wanted to leave, even though authorities made it clear that he who stays does so at his own peril.”

Torrential rains began in the afternoon, and emergency officials said they had evacuated more than 4,250 people in coastal towns and set up 58 shelters before the dangerous storm.

The storm also battered the Islas Marias, a group of Mexican islands about 60 miles (100km) off the mainland that include a nature preserve and a federal prison. Federal authorities declined to comment on precautions that were taken at the prison, citing security concerns, but said the safety of prisoners was a priority.

As Willa closed in, the beach in Mazatlan almost disappeared, with waves slamming against the coastal boulevard under looming black clouds. A few surfers took advantage of the high waves even as workers boarded up windows on hotels, shops and homes. Schools were closed and the streets nearly empty.

Some families went to a Mazatlan convention center, which opened its doors as a shelter. They spread out blankets along the walls and waited for the storm. “The house we’re living in is not well built,” said Sergio Ernesto Meri Franco, who rents a studio apartment.

The federal government issued a decree of “extraordinary emergency” for 19 municipalities in Nayarit and Sinaloa states.

Farther south, the remnants of tropical storm Vicente brought heavy rain that caused deadly flooding and mudslides. Federal disaster agency chief Luis Felipe Puente said 11 people had died as a result of Vicente. Local officials earlier put the figure at 12.