AFP - Hurricane Jimena on Monday roared toward Mexico's Baja California as an extremely dangerous Category Five storm, Mexican officials said as they planned emergency evacuations for 20,000 families in its path.
   
Jimena was packing winds of up to 155 miles per hour (250 kilometers per hour) but was expected to weaken slightly before making landfall in Baja California late Tuesday or early Wednesday, the National Weather Service said.
   
The center of the hurricane was 285 miles (460 kilometers) south of Cabo San Lucas as of 0001 GMT Tuesday, said the US National Hurricane Center (NHC), an American agency which tracks and predicts storms.
   
US forecasters put Jimena at a Category Four on the Saffir-Simpson scale, on which five is the strongest rating, but noted that the storm was "very near the threshold of Category Five status."
   
Residents of the northwestern peninsula frantically boarded up their homes and stockpiled goods as the most powerful hurricane of the year -- the only one to reach Category Five -- approached.
   
Jimena forced a major international conference on tax transparency to be moved from Los Cabos, a resort town on the southern tip of Baja California, and set up in Mexico City instead.
   
The Paris-based Organization for Economic Co-operation and Development (OECD) said it had moved the event because of the "threat of severe damage posed by Hurricane Jimena."
   
Baja California, a peninsula which spears south from California into the Pacific, was placed on high alert as emergency officials prepared contingency plans.
   
Francisco Cota, the head of the civil protection agency in Los Cabos, said any evacuation plan would focus on densely populated areas and valleys at most risk of flooding.
   
"It will place special emphasis on the more than 20,000 families who live in high-risk areas," he told journalists after a meeting of civil defense officials.
   
The US State Department issued an alert to American citizens urging them to seriously reflect before risking travel to areas of Mexico and the United States lying in its path.
   
"US citizens located in areas likely to be impacted by Hurricane Jimena and who do not have access to adequate and safe shelter should consider departing while commercial flights are still available," the warning said.
   
With gusty winds and rains already hitting La Paz, the capital of the peninsula's southern Baja California Sur state, residents were hastily boarding up windows and stocking up on groceries before the shops closed.
   
"Jimena is moving toward the northwest near 10 miles per hour... and a turn toward the north-northwest with a gradual increase in forward speed is expected over the next day or so," the NHC said.
   
"On the forecast track Jimena will be approaching the southern portion of the Baja California peninsula on Tuesday."
   
The Miami-based agency said that although the strength of Jimena would fluctuate over the next day or so it was guaranteed to make landfall as a major hurricane.
   
"A dangerous storm surge along with battering waves will produce significant coastal flooding along the Baja California peninsula. Preparations to protect life and property should be rushed to completion," the NHC warned.
   
Flooding and landslides have already been reported at the weekend in southern Mexican states as the hurricane churned its way up the country's Pacific coast.
   
Another storm, Kevin, way to the west of Jimena in the Pacific, had weakened considerably and no longer posed a threat, according to the NHC, which also warned Monday that a tropical depression may be developing east of the Lesser Antilles in the Caribbean Sea.