Hurricane Cristina has rapidly strengthened to a major Category 4 storm off Mexico's Pacific coast.

The hurricane's maximum sustained winds increased to near 230 km/h Thursday morning. The hurricane reached Category 4 strength just hours after becoming a Category 3 storm.

The U.S. National Hurricane Center says some additional strengthening is possible during the day but weakening is expected to begin Thursday night.

Cristina is centred about 400 kilometres southwest of Manzanillo, Mexico, and is moving west-northwest near 13 km/h.

There are no coastal watches or warnings in effect, but forecasters say swells generated by the hurricane are affecting parts of Mexico's southwest coast and could cause life-threatening surf and rip current conditions.