No one has claimed responsibility for the attacks. However, police said that attacks bore some resemblance to the Bangladeshi group Harkat-ul-Jihad al-Islami, which wants the secession of the disputed Himalayan region of Kashmir.
Al Jazeera's Todd Baer, reporting from Delhi, said all schools and commerical complexes in Bangalore have been closed.
"The city has quite literally been paralysed," he said.
Two blasts occurred close to police facilities while another bomb went off in a city-centre business district.
The fourth explosion targeted the Koramangla district, where several computer software firms are located.
The other blasts occurred in the southern suburbs of Bangalore, a religiously mixed city, which is the capital of Karnataka state.
Madhukar Gupta, the Indian home secretary, said the blasts occurred within a radius of 10 to 15km.
A. Raghuveer, the assistant police commissioner, said: "Some of the blasts are low intensity using gelatin [gelignite explosive] sticks".
Television footage showed bomb squads scouring the areas with sniffer dogs. Some of the sites were covered with shattered glass.
Ramesh, a software engineer, told the AFP news agency that he was hit by flying shrapnel as he was riding his motorcycle.
"We saw smoke and dust and then some object pierced my leg," he said.
India has been struck by bombings in recent years, with targets ranging from mosques and Hindu temples to trains.
Bangalore is home to more than six million people and some 1,500 domestic and foreign firms.