A powerful cylone has swept across Mexico's northwest Pacific coast, tearing off roofs and forcing hundreds of people to flee flooded homes, local authorities say.

One person has gone missing and more than 20,000 homes are without electricity since Hurricane Norbert struck on Saturday.

Norbert, which made landfall as a Category Two hurricane on the five-level Saffir-Simpson scale, came ashore at Puerto Cortes on the Baja California peninsula around 1630 GMT, according to Mexico's national weather service.

It was later downgraded to a Category One storm with winds of 150km per hour.

"A man trying to cross the Miramar creek has been reported as missing after the current swept him away," the authorities in Loreto, one of the Mexican municipalities Norbert tore through, said.

At 0300 GMT on Sunday the eye of Norbert was located about 195km east-northeast of Loreto, the US-based National Hurricane Center reported.

Mass evacuations

Some 2,850 people were housed in temporary shelters.

Forty per cent of homes were totally or partially damaged on the islands of Margarita and Magdalena, mainly having lost their roofs, according to a report from state protection services.

In the Baja California capital of La Paz, the storm knocked out power to 13,000 homes, and to 8,000 more in Ciudad Constitution, the Federal Electricity Commission reported.