Some passengers reportedly jumped from speeding trains in panic.
Maharashtra state Chief Minister Vilasrao Deshmukh said after meeting with his Cabinet that the death toll was 147, with 439 others wounded, as of Tuesday night.
In Washington, the State Department said it had no information about whether there were any American casualties.
All of India's major cities were reportedly on high alert following the attacks, which came hours after a series of grenade attacks by Islamic militants killed eight people in the main city of India's part of Kashmir.
Reflecting the fears of coordinated or copycat bombings throughout the world, even New York City increased its transit security Tuesday with hundreds more officers patrolling the subways and more random bag searches.
"We take a terror attack in any place in the world, especially one on a public transport system, as a serious warning," New York Mayor Michael Bloomberg said.
Commuter transit systems have been tempting targets for terrorists in recent years, with bombers killing 191 in Madrid in 2004 and 52 in London last year.
Bombay suffered blasts in 1993 that included the Bombay Stock Exchange, killing more than 250 people.
A senior Bombay police official, P.S. Pasricha, said Tuesday's explosions were part of a well-coordinated attack.
Police reportedly carried out raids across the country following the blasts. One TV station said a suspect was in custody.
India and Pakistan have fought three wars since the subcontinent was partitioned upon independence from Britain in 1947, two over Kashmir.
Dozens of militant groups have been fighting Indian rule in Kashmir, demanding the largely Muslim region's independence or merger with Pakistan. New Delhi has accused Pakistan of training, arming and funding the militants. Islamabad insists it only offers the rebels diplomatic and moral support.
Pakistani President Gen. Pervez Musharraf offered condolences over the loss of life Tuesday, his Foreign Ministry said, adding: "Terrorism is a bane of our times and it must be condemned, rejected and countered effectively and comprehensively."
Accusations of Pakistani involvement in a 2001 attack on India's parliament put the nuclear-armed rivals on the brink of a fourth war. But since then, Pakistan and India have embarked on a peace process aimed at resolving their differences, including the claims to all of Kashmir.
In Washington, a U.S. official who spoke on condition of anonymity because the events were still unfolding said the coordination of Tuesday's attacks and the targeting of trains at peak travel times match the modus operandi of two Islamic groups active in India during the last several years: Lashkar-e-Tayyaba and Jaish-e-Mohammad. The U.S. government has designated both terrorist organizations and considers them affiliates of al-Qaida.
<<AP Online -- 07/12/06>>