The blasts took place in Malegaon, 260km northeast of Mumbai, India's financial hub.
Police said the explosions occured as thousands gathered at a burial ground for special Friday prayers.
Indian television reported that three explosions took place, two in the burial ground crowded with worshippers and a third in the town square.
India has been on a heightened security alert after a series of bombs on commuter trains in Mumbai killed 186 people in July.
Friday's blasts came days after Manmohan Singh, India's prime minister, said that intelligence agencies had warned of more Islamic terrorist attacks across the country, possibly on economic and religious targets as well as on nuclear installations.
That attack was blamed on extremist Islamist groups with links across the border in Pakistan.
Malegaon has suffered religious violence in the past.
In May, police recovered a cache of explosives and automatic rifles from the region based on information they said was provided by arrested extremist Islamists.