While authorities reportedly say there may be more suspects linked to the alleged terrorist plot uncovered in the city, Police Commissioner Ray Kelly has reassured New Yorkers that it poses no threat to the city at large.
Officials reportedly say there may be 16 to 20 more suspects who are connected to the 24-year-old former Queens resident Najibullah Zazi.
There were also reports of law enforcement officials visiting fertilizer manufacturers and storage facilities which could potentially serve as bomb making factories.
Authorities believe Zazi was trained in an Al-Qaida camp in Pakistan. He appeared in federal court in Colorado Monday with his father, Mohammad, and they are both charged with lying to authorities.
Zazi's laptop alleged has instructions on how to make bombs. Backpacks and cell phones were also seized last week from apartments in Queens where Zazi visited.
Backpack bombs were used in the terrorist attacks carried out in Madrid and London in 2004 and 2005.
A judge ordered Zazi held until a bail hearing on Thursday.
Meanwhile, Kelly says the city is already at a security level that exceeds cities around the world, and that has not changed as a result of two FBI bulletins warning about terror plots.
"We have not engaged in any different practices or increased our security," said the police commissioner. "As I say, we do a lot every day, devote over 1,000 police officers every day to protect this city from a terrorist threat, so we have not increased that number of resources."
MTA officials also say there is "no credible threat" to the transit system and that they are in constant contact with federal, state and local law enforcement.
The FBI and the Department of Homeland Security have issued two security bulletins about general terrorist interest in attacking stadiums, hotels and entertainment venues. Federal officials are also warning mass transit systems around the country to be on the alert.
"We have kept at a higher level for a long time, so we didn't have to change anything," said the mayor, "but I think the increase in security that the federal government's called for in most places really is merited. We've always thought so and I'm glad to see that others are thinking so as well."
The New York City Police Department says it's already put extra attention on the subway tunnels, ventilation system, and certain emergency exits since the London bombings in 2005.
Security experts agree that the subway can be especially vulnerable to terrorist attacks.
"If you think about the impact of an explosive on the ground versus an explosive in a bus, we have different types of casualties," said Professor Maki Haberfeld of John Jay College.
Yet commuters told NY1 Tuesday that they are still going about their daily routines.
"I really haven't put any more thought into it," said one New Yorker. "You hear about it so often, it's kind of like, more terrorism news."
"I'm not more concerned than I ever was," said another. "Look man, if it's going to happen, it's going to happen. There ain't nothing that the NYPD can do, or anyone else."
"I'm a little scared but I'm not going to modify my plans because if you do that, then you let the people who are trying to scare us win," said a third.
Federal officials say it is not uncommon for these notices to be issued and they are not supposed to be for the public.
Meanwhile, a Queens imam accused of tipping off the Zazis appeared in federal court in Brooklyn Monday.
Ahmad Wais Afzali did not formally enter a plea, but his attorney says his client did not lie to authorities who were trying to piece together details of the alleged bomb plot.
"Why in the world would he lie to the FBI about the contents of an investigation he knew they had on tape?" asked his attorney Ron Kuby.
Afzali will be held until Thursday, when a detention hearing will take place.