MEXICO CITY (AFP) - Fast-moving Patricia grew into an "extremely dangerous" major hurricane off Mexico's Pacific coast on Thursday, forecasters said, warning of possible landslides and flash flooding.

The US National Hurricane Centre said "preparations should be rushed to completion" as Patricia increased ominously from a category two to a category four storm in the five-level Saffir-Simpson scale.

Packing maximum sustained winds of 215kmh, the hurricane was expected to strike the coast on Friday afternoon or evening, the Miami-based centre said.

"Some strengthening is forecast tonight and Patricia is expected to remain an extremely dangerous hurricane through landfall," it said in a statement.

Emergency services personnel were being moved from other states to the threatened region, said Mexico's National Water Commission director Roberto de la Parra.

"It is moving much faster than hurricanes we have had in the past," de la Parra told a news conference.

Mexican officials closed schools in Colima and Guerrero state.

Two dams in Jalisco and Michoacan were being drained to prevent flooding while residents were advised to protect their windows with large tape in the form of a cross.

The Jalisco state government urged the coastal population to avoid the coast.

The region includes the major port of Manzanillo, Colima state, and the tourist resort of Puerto Vallarta in Jalisco.

At 2100 GMT (5am on Friday Singapore time), Patricia was 400km south of Manzanillo, according to the US hurricane centre.

The storm was moving west-northwest at 20kmh.

Patricia is expected to produce 15cm to 30cm of rainfall accumulations over the states of Jalisco, Colima, Michoacan and Guerrero, which could produce flash floods and mudslides, the US centre said.

The storm surge could also produce coastal flooding, accompanied by "large and destructive waves," it warned.

The water commission warned that rivers could rise and roads could be affected by the bad weather.

WIND FORCE CAUSES CONCERN

Mexico's interior ministry activated its emergency response committee to coordinate the response.

Officials said nearly 1,800 shelters for 259,000 are available, but no evacuations have been ordered so far.

"The amount of water and the strength of the wind worry us," national civil protection coordinator Luis Felipe Puente told a news conference.

Jalisco, Michoacan, Colima and Nayarit are expected to get the equivalent of 40 per cent of their annual rainfall in the next 48 hours, the water commission said.

Mexico faces the double threat of Atlantic and Pacific tropical storms during the hurricane season, which ends Nov 30.

In 2013, twin storms Ingrid and Manuel nearly simultaneously struck each coast, leaving 157 people dead in a rare double onslaught.