MUMBAI, India — Three explosions have shaken India's commercial capital Mumbai, with reports saying at least 20 people have been killed.

The chief minister of Maharastra, Prithviraj Chavan, said 21 people had been killed and 113 wounded in three explosions during rush hour, the AP reported.

(Photo Gallery: Indian police officers look for clues at the blast site)

Two of the blasts were in south Mumbai, Reuters reports, while one was in downtown Mumbai. The BBC reported the explosions as taking place in the famed jewelry market Zaveri Bazaar, another near the Opera House.

(Read More: Indian train bombers captured, say police)

India's Home Ministry called the explosions a terror attack, the first major attack on Mumbai since 10 Pakistani militants went on a 60-hour rampage at luxury hotels, the train station and a Jewish center in 2008, killing 166 people.

The Indian government blamed that attack on the Pakistani-based militant group Lashkar-e-Taiba, and accused Islamabad of aiding the gunmen.

The Pakistani government was quick to issue a statement condemning Wednesday's attack, ABC reports.

The Guardian quoted the Home Minister, P. Chidambaram, as saying the entire city had been put on "high alert," while the U.S. consulate in Mumbai reportedly released a statement reminding U.S. citizens "to exercise prudence."

President Barack Obama called the bombings "outrageous" and pledged U.S. support for the Indian government, the ABC reports.

TV footage showed scenes of apparent chaos Wednesday.

One (very graphic) video posted on YouTube is said to have been taken at the Zaveri Bazaar.

New Delhi says Pakistan-based terrorist groups train militants to carry out attacks against India, the Globe and Mail reports. Islamabad has rejected the claim.

Home-grown militant groups are also active in the country and have in the past few years carried out attacks in large cities.

GlobalPost's Mumbai correspondent, Hanna Ingber Win, says that Mumbaikars have reacted with anger and sadness, though very little surprise.