President Barack Obama says the killing of Osama bin Laden sends a message to the world and the country that "when we say we will never forget, we mean what we say".

Obama made his remarks as he visited a New York fire station that lost 15 men during the September 11, 2001 terrorist attack.

Obama visited Engine 54 at Engine 54, Ladder 4, Battalion in the city's theatre district in Midtown Manhattan.

It was the first stop on his trip to New York where he will lay a wreath in memory of the 9/11 victims in the wake of the shooting of Osama bin Laden.

The fire station contains a memorial for the dead firefighters that includes messages from their families.

"This is a symbolic site of the extraordinary sacrifice that was made on that terrible day," the president said after shaking hands with firefighters.

"What happened on Sunday because of the courage of our military and the outstanding work of our intelligence sent a message around the world but also sent a message here back home," he said.

Obama said he hoped the outcome brought the firefighters "some comfort," thanked them for their daily sacrifice and said they had a president and administration that has "got your back."

In his brief remarks, the president never mentioned bin Laden's name.

Former New York Mayor Rudy Giuliani, who led the city in dark days after the attacks, joined Obama in the visit to the station.

The president viewed a bronze memorial plaque commemorating the firefighters who were lost and then lunched privately with a dozen firefighters.

From there, Obama was to travel to ground zero where the World Trade Centre's twin towers once stood.