The storm is seen as “potentially catastrophic” in its impact.
Mexican authorities have already been evacuating thousands of residents along the country’s Pacific coast.
The storm is comparable to Typhoon Haiyan, which killed 6,300 people in the Philippines in 2013, the World Meteorological Organization says.
A state of emergency has been declared in three states in Patricia’s path.
It made landfall in the Cuixmala area of Jalisco state, some 85km (55 miles) from the port city of Manzanillo.
The US National Hurricane Center in Miami said it hit the coast with winds of 265km/h (165mph).
Video filmed in Manzanillo an hour before the hurricane struck shows trees bending in severe wind.
Hurricane Patricia: Key questions
The centre said that Patricia was the strongest storm it had recorded in the eastern Pacific or the Atlantic.
It has already produced the third lowest barometer reading ever recorded – a pressure of 880 millibars at the centre of the storm – the centre reported.
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Some 400,000 people live in vulnerable areas, according to Mexico’s National Disaster Fund.
The hurricane, which will bring torrential rain, could trigger flash floods and mudslides, the US centre said.
It also warned of potential flooding from the sea and destructive waves.