Blanca mushroomed into a major hurricane off Mexico's Pacific coast on Wednesday but could weaken before making landfall in the tourist-friendly Baja California peninsula, forecasters said.

The storm's maximum sustained winds reached 220 kilometers (140 miles) per hour and it was "barely moving" some 745 kilometers (465 miles) southwest of Zihuatanejo, Guerrero state, according to the US National Hurricane Center.

Blanca became a category four hurricane, the second most powerful on the five-level Saffir-Simpson scale, and the center said some additional strengthening is forecast in the next 24 hours.

But a five-day forecast map shows Blanca weakening to tropical storm strength when it touches the southwestern coast of Baja California on Monday. The center had previously forecast Blanca to strike on Sunday, when Mexicans vote in midterm elections.

Blanca would make landfall north of the Los Cabos resorts that were ravaged in September by Hurricane Odile. It caused millions of dollars in damage and left six people dead.

Authorities in Los Cabos said they were monitoring Blanca's progress. The hurricane was 1,300 kilometers (810 miles) from Cabo San Lucas Wednesday afternoon.