(Photo: Xinhua/AFP)

New York City heightened security over its public transportation infrastructure, from trains to buses, tunnels to waterways, following a series of bombings on London's public transit system Thursday.

At a news conference, Governor George Pataki, Mayor Michael Bloomberg and Police Commissioner Raymond Kelly outlined the steps that had been taken: holding over the overnight police shift to increase the number of officers on duty, police and Coast Guard escorts for Staten Island ferries, helicopters over the harbors, monitoring subway tunnels that cross the rivers 24 hours a day.

But they also encouraged New Yorkers to go about their business, while keeping an eye out on their surroundings.

"Go about your life, and when you see something suspicious turn it over to the professionals," said Bloomberg, who returned to New York from Singapore, where he had been pushing for the city to be named host of the 2012 Olympic Games, a position that eventually went to London.

Pataki said he had ordered state troopers to ride mass transit and had signed an executive order giving local law enforcement authority to New Jersey and Connecticut police riding on New York trains. Kelly said there would be an officer on every train for the rush hour on Thursday and Friday.

The terror alert for mass transit systems across the United States had been raised to orange or "high" in the wake of the London blasts.

But unlike the rest of the country, New York has been on orange alert ever since the Sept. 11 attacks. Bloomberg acknowledged that many New Yorkers seeing the television footage of the London blasts would worry of a similar attack in their own city.

"We are doing everything in our power to prevent that from happening," he said.

About 4.5 million passengers use New York's subways daily, and the metro area transportation system of commuter rails, subways and buses is the largest in the country.

City commuters, while admitting to some nervousness, didn't let news of the explosions alter their travel routes.

"My antennae is definitely up," said Kevin Kehoe, a 45-year-oldcreative director who traveled in from Westchester on the Long Isalnd Rail Road with his wife en route to lower Manhattan.

"You have to be alert. That's a hard thing to pinpoint, but you have to at least try," he said.

"I've always been aware that the subway could be a target but it hasn't affected the way I live my life," said Mary Ellen Kelly, a Manhattan commuter.

Security was also beefed up on the city's roadways. One lane leading from BQE West into Williamsburg Bridge was closed, slowing traffic to a crawl. A police cruiser was sitting near entrance on Brooklyn side this morning, a sight that was common on high alert days, but that has not been seen for weeks.