"We are stepping up security throughout," a police spokesman said. Duty officers would be required to extend their shifts to provide extra personnel during the evening rush hour.
The frequency of random bag searches on the subway will also be expanded. The bag searches were introduced last year in the wake of the July 7 bombings on the London transport system.
New York has remained on a heightened state of terror alert ever since the September 11 attack on the World Trade Center.
Recent years have seen specific alerts sounded over a possible terror attack on the city's transit system which carries 7.7 million commuters on an average working day.
Only last week, the FBI said it had foiled a terror plot by a group of
Al-Qaeda followers to carry out suicide attacks on train tunnels in New York and New Jersey.
In Washington, US Secretary of State Condoleezza Rice condemned the blasts, which ripped through rush-hour trains in Mumbai, as "horrific."
"Let me just say that we condemn thoroughly this terrible terrorist incident," Ms Rice told reporters before a meeting with Serbian Prime Minister Vojislav Kostunica.
She said the United States had "great sympathy" for the families of those killed and vowed: "We will stand with India on the war on terror."
"It simply shows that this kind of hideous incident can happen anywhere in the world against innocent people, and so we stand with India in this time of need."
The State Department said the US government had already been in touch with the Indian government to offer any assistance needed, noting that an investigation had been opened into the attacks, which killed at least 163 people and wounded 464 others.
So far, two Americans were known to have been injured in the attacks but a final tally of casualties has still not been made.
Calls of condemnation also rang out from the US Congress, where Senate majority leader Bill Frist condemned the "cowardly and barbaric act."
"On behalf of my Senate colleagues and the American people, I express my deepest sympathies to the victims, their families, and to the people of India."
Leading Democratic lawmaker Tom Lantos said that after the bombing, the United States and India "have fresh incentives to forge ever closer ties."
"And should the Indian government ask for assistance with the investigation, I call on the United States government to underscore the importance of these ties by committing every available resource to get to the bottom of this latest outrage," Congressman Lantos said.