NEW YORK – City officials ordered nearly 300,000 residents to leave waterfront neighborhoods and announced the impending shutdown of the city’s vast transit system, two unprecedented precautionary steps forced by the threatened fury of Hurricane Irene.

 “You only have to look at the weather maps to understand just how big this storm is, and how unique it is. And it’s heading basically directly for us,” Mayor Michael Bloomberg said at a news briefing Friday afternoon. “This is very serious. Do not be fooled by the sun outside. You just can’t wait until gale force winds and driving winds begin.”

Irene will likely be a Category 1 hurricane when it reaches the city but it will bring high winds and 8 to 12 inches of rain, Bloomberg said.

“We’ve never done a mandatory evacuation before now and we wouldn’t be doing it if we didn’t think this storm is going to be serious,” he said.

Nursing homes and five hospitals in low-lying areas of the city began evacuating Friday. Residents of coastal areas including Brooklyn’s Coney Island and Rockaway Peninsula and the Battery Park City neighborhood in Manhattan must leave for higher ground by 5 p.m. Saturday, Bloomberg said.

“We don’t have the manpower to go door-to-door and drag people out,” Bloomberg said. But, he added, ignoring the evacuation order means “people might die.”

As officials continued with dire warnings, the city’s activity began to grind to a halt in the face of the approaching hurricane.

Street fairs and outdoor festivals scheduled for Sunday have been canceled as the city yanked permits. City beaches have been closed. The Bronx Zoo announced it will close.

The hurricane even interfered with Broadway: All weekend shows were cancelled.

The New York Mets’ Saturday and Sunday games with the Atlanta Braves have been postponed. All city construction, including work to rebuild the World Trade Center site, was suspended from Saturday until 7 a.m. Monday.

The storm seems to have gained New Yorkers‘ attention: traffic on the city’s website,, where evacuation information is posted, spiked to 4.3 million visitors Thursday, temporarily crashing it. The previous high had been 2.2 million in January.

The city’s subway and bus systems will begin shutting down at noon on Saturday, as will suburban rail systems that serve Long Island and the northern suburbs, said Jay Walder, chairman of the Metropolitan Transportation Authority. Shutting down the sprawling system and moving equipment to safe territory is expected to take roughly eight hours. Bus and subway service halted during a 2005 transit strike, but the entire system has never been halted before.

“I cannot stress enough, please do not wait for the last train,” Walder said.

The hurricane’s anticipated size and strength is expected to make a speedy restart of the mass transit system challenging, Walder said.

Falling trees and limbs could block tracks on the sprawling system, and the system’s 13 under-river tunnels could flood, he warned.

“I don’t think there’s any question that the period after the storm is going to be difficult,” he said.

City officials did not issue any immediate restrictions on car travel. Taxi service will continue to operate unless hurricane conditions make it too dangerous to drive.

The city “will take a hard look” at closing municipal-operated bridges if sustained hurricane wind speeds reach 50 mph, Bloomberg said. The Port Authority of New York and New Jersey and the Triborough Bridge and Tunnel Authority, operators of the city’s major bridges and tunnels, will make independent decisions on whether to close any of those facilities, he said.

If winds reach 50 mph, ferry service to Staten Island will be suspended, Walder said.

Gov. Andrew Cuomo called out the National Guard, sending more than 900 soldiers and 100 vehicles will head to the Hudson ValleyNew York City and Long Island on Saturday in response to the storm.

Bloomberg urged New Yorkers and visitors to remain indoors from 9 p.m. Saturday to 9 p.m. Sunday.

“Stay inside on Sunday. It’s a good time to catch up or sleep late,” he said.

“We can joke about this on Monday morning, but until then it’s a matter of life and death.”