A series of bomb blasts have rocked India's high-tech capital Bangalore - killing at least two people and injuring a dozen more.

Police search for clues in Bangalore

Police said the city was on high alert for more attacks, with bomb disposal teams and forensic experts rushed into action.

Authorities are trying to determine who was responsible, while IT companies closed early in the city.

"A woman and a man have died and around a dozen others received shrapnel injuries in the blasts," Bangalore police commissioner Shankar Bidri told reporters.

The officer put the number of explosions at seven but the Press Trust of India news agency quoted unnamed officials saying there were nine blasts.

Two occurred close to police facilities while another bomb went off in an upmarket city-centre business district. A fourth explosion targeted Koramangla district, which houses several computer software firms.

Other blasts were reported from the southern suburbs of the religiously mixed and cosmopolitan city, also the hub of India's burgeoning outsourcing and software industry, police said.

"We suspect that timer devices were used in two or three explosive devices, while the others could have been set off using mobile phones," police chief Bidri said.

"We are investigating the blasts. Bomb disposal squads and forensic experts have reached the spot. Bangalore police is on high alert."

So far none of India's various Islamic guerrilla groups or outlawed Maoist insurgents have claimed responsibility for the attacks.

Indian Prime Minister Manmohan Singh condemned the serial bomb blasts and urged residents to "remain calm and maintain communal harmony," a spokesman of the premier said in New Delhi.

"The prime minister also expressed grief over the loss of lives and sends his condolences to the families of the bereaved," the spokesman added.

Bangalore is home to more than six million people and some 1,500 domestic and foreign firms.