Hurricane Hilary was downgraded to a Category 2 tropical storm on Saturday as it moved towards the Baja California peninsula in Mexico.

But forecasters still consider it to be a dangerous weather event that is expected to bring "catastrophic" flooding to northwestern Mexico as well as southern California, where it will be the first such tropical storm in 84 years.

"This does not lessen the threat, especially the flood threat," said Jamie Rhome, deputy director of the US National Hurricane Center (NHS).

"Don't let the weakening trend and the intensity lower your guard."

The NHS added that "locally catastrophic" flash flooding is expected, "especially in the northern portions of the peninsula."

Wild weather begins in Mexico

As Hilary pummeled Mexico's Baja California peninsula with rain, one person drowned in the town of Santa Rosalia when their vehicle was swept away by an overflowing stream.

Rescue workers managed to save four other people around the nearby township of Mulege.

Authorities in Mexico's second largest city, Tijuana, have moved some residents to temporary shelters as the threat of landslides looms.

"If you hear noises, or the ground cracking, it is important for you to check it and get out as fast as possible, because the ground can weaken and your home could collapse," said Rafael Carrillo, head of the Tijuana fire department.

Meanwhile, Mexico's navy evacuated 850 people from islands off the Baja coast and deployed 3,000 troops around the region.

California residents filled sandbags as Hurricane Hilary approached Mexico Deutsche Welle

Preparations underway in the US

In the US, California Governor Gavin Newsom declared a state of emergency on Saturday and officials urged people to finish final preparations for the storm, saying that leaving it until Sunday would be too late.

Nancy Ward, director of the California Governor's Office of Emergency Services, said Hilary could be one of the worst storms to hit the state in more than a decade.

"Make no mistake, this is a very, very dangerous and significant storm," she said.

The US Federal Emergency Management Agency (FEMA) said it deployed teams to areas in Hilary's path and is providing President Joe Biden with regular updates.

"He has encouraged everyone to make sure that they are aware of what this dangerous storm is potentially going to bring and to listen to their local officials on the steps they can take to make sure that they are keeping safe," FEMA chief Deanne Criswell said.