At least 15 people have been killed and 50 injured in three blasts that rocked India's financial hub of Mumbai in the bustling evening hours on Wednesday, according to unofficial estimates.

Mumbai police have confirmed that Improvised Explosive Devices (IED) were used in the blasts, which took place in Dadar, Saveri Bazar and Opera House between 6 and 7 PM local time. The Union Home Ministry has confirmed the explosions are terror attacks.

India's elite security forces, the National Security Guard, (NSG), has been put on alert, and the National Investigation Agency officials have been dispatched to Mumbai.

Witnesses have said at least 6 people died in the blast, which took place in a bus stop.

The Union government has not yet revealed its estimate of the number of people dead, but TV channels say between six and 15 people have died. According to Asianet News, at least 15 people have died.