MEXICO CITY -- Tropical Storm Hilary strengthened into a hurricane early Thursday off Mexico's Pacific coast and could become a major hurricane as it heads north over the ocean.

The U.S. National Hurricane Center said Hilary's strength was rapidly intensifying. It had maximum winds of 85 mph (140 kph) and is expected to cause rainfall across the Baja Peninsula and the U.S. Southwest on Friday through early next week.

It was located 365 miles (590 kilometres) from Cabo Corrientes in Mexico, still far from land.

The hurricane was moving west-northwest at 14 mph (22 kph) and was expected to become a major hurricane by Thursday night or early Friday as it moves toward the Baja Peninsula, near the U.S. border.

Hilary could bring rain to some portions of southern California and southern Nevada, according to the hurricane centre.