Hurricane Dolores formed off Mexico's Pacific coast on Monday, threatening to dump heavy rains in several states, authorities said.

Dolores packed maximum sustained winds of 120 kilometers (75 miles) per hour as it moved parallel to the coast, some 305 kilometers southwest of the port of Manzanillo, the US National Hurricane Center said.

The former tropical storm could mushroom into a major hurricane by Wednesday, the center said.

Mexico's National Weather Service said heavy rains are expected in Michoacan, Colima and Jalisco.