MEXICO CITY (AFP) - Hurricane Willa surged to a dangerous Category Four storm on Sunday (Oct 21) off Mexico's Pacific coast, United States forecasters said.

"Extremely dangerous... Hurricane Willa continues to rapidly strengthen (and is) forecast to produce life-threatening storm surge, wind and rainfall over portions of south-western and west-central Mexico, beginning on Tuesday," the Miami-based National Hurricane Centre (NHC) warned.

The monster storm was 365km south-southwest of Cabo Corrientes, Mexico, packing top sustained winds of 220kmh.

It was churning forward north-northwest, at a slow 9kmh, the forecast said.

"Additional strengthening is expected during the next day or so, and Willa is forecast to be a dangerous hurricane when it reaches the coast of Mexico," the NHC said.

Mexico's government has put various parts of the coast on alert.