People evacuate apartment buildings in Manhattan's Battery Park on Saturday....

People evacuate apartment buildings in Manhattan's Battery Park on Saturday. New York City ordered more than 300,000 people who live in flood-prone areas to evacuate as Hurricane Irene is forecast to reach the city. (Aug. 27, 2011) Credit: Getty Images

New York City for the first time ordered a mandatory evacuation of low-lying areas by Saturday afternoon, including the financial district, Battery Park City, Coney Island and all of the Rockaways.

"Don't be fooled by the sun outside," Mayor Michael Bloomberg said during a news conference Friday at City Hall. "You have to start your preparations to leave right now."

Complicating the evacuation of almost 300,000 people is the shutdown beginning at noon Saturday of the city's mass transit system, including subways, buses and commuter trains. Metropolitan Transportation Authority chief Jay Walder said it would take about eight hours to shut down the transit system.

"Don't wait for the last bus," Walder warned at the briefing.

As a result of the public transit suspension, all Broadway performances on Saturday and Sunday were canceled.

The evacuations affect all so-called Zone A areas, which are the most flood-prone, low-lying coastal areas of the five boroughs. Mandatory evacuation also extends to Zone B areas of the Rockaways. The mandatory evacuation should be completed by 5 p.m. Saturday, officials said.

By 5 p.m. Friday Battery Park City was in evacuation mode. More than 200 uniformed police officers were assembling nearby for duty by the World Financial Center. Residents were lining up at a taxi stand with luggage.

But Robert Dziedzic, 54, a 25-year resident and real estate agent, said he was staying put.

"What's the point. I've already been through that," he said, pointing to Ground Zero, where the World Trade Center once stood. "I'll ride this one out with a few cocktails."

Bloomberg said violating a mandatory evacuation order could be a misdemeanor but added that no one is likely to be arrested.

Some 91 emergency facilities, a combination of evacuation centers and emergency shelters, opened Friday and will be able to handle 71,000 people, the mayor said.

At the September 11 Memorial, which Bloomberg said will open on schedule in two weeks, officials reported they were pruning the plaza's 400 oak trees, removing or securing loose equipment, and bringing in emergency generators to help pump water from the site should it flood.

Roads will be open, but Bloomberg said if sustained winds hit 50 mph, the city would close its East River spans, the Brooklyn, Williamsburg, Manhattan and Queensboro bridges.

Winds of more than 60 mph would shut down of the George Washington, Verrazano-Narrows, Robert F. Kennedy, Bronx-Whitestone, Throgs Neck and Henry Hudson Bridges.

If sustained winds hit 46 mph, the city will stop Staten Island Ferry service, Bloomberg said.

With Emily Phan Ngo

and Maria Alvarez