The extra police forces were deployed after officials briefed President Barack Obama of the situation and New York Mayor Michael Bloomberg disclosed that the terror threat to the city is "credible but not corroborated".
"The President directed the counter-terrorism community to redouble its efforts in response to this credible but unconfirmed information," a White House official said.
The threat was received by the US intelligence agency on Wednesday and the officials have put a look out notice for three people, who entered the country last month by air traveling from Afghanistan via a third country.
Counter-terrorism officials were assessing the report and media reports said that authorities were contemplating raising the threat level in New York and Washington.
The agencies are also pursuing the leads overseas in an effort to unravel the plot, a statement by a spokesman for the department of Homeland Security said.
Further, a nationwide hunt has been launched for at least two missing rental trucks that remain untraceable from locations in Kansas City, Missouri, officials said.
The scare came days ahead of anniversary ceremonies for the 9/11 attacks when President Obama and his predecessor George W Bush are due in the city, along with large crowds.
On September 11, 2001, two hijacked planes hit New York's World Trade Centre, turning the iconic twin towers to rubble, a third plane plowed into the Pentagon and the fourth plane crashed into a field in Pennsylvania.