Most of the detentions were made overnight in Malwani, a northeastern suburb of Bombay, said police Inspector S. Goshal. He said none of them has been formally arrested or charged, and they were rounded up only for questioning to help with the investigations into Tuesday's serial bombings.
Prime Minister Manmohan Singh was scheduled to visit Bombay on Friday for an assessment of the investigations into the bomb blasts, which officials say could have been carried out by Kashmiri militants.
In New Delhi, Singh's Cabinet issued a statement Thursday, saying the government is committed to combating terrorism.
Bombay police Commissioner A.N. Roy confirmed a large number of detentions have been made but refused to give an exact figure, according to the AP.
He said those arrested include known thugs, gangsters and trouble makers, who might have information about the culprits.
The arrests came a day after the police chief of Maharashtra state, of which Bombay is the capital, said investigators were looking into a possible link with Lashkar-e-Tayyaba, one of the several Kashmiri militant groups fighting for independence from India for the Himalayan region.
Lashkar has in the past employed near-simultaneous explosions to attack Indian cities. A spokesman for Lashkar, Abdullah Ghaznavi, denied the group was involved, saying in a statement that "Indian security forces blame Lashkar in an attempt to defame Kashmir freedom struggle."