One person was killed when half-a-dozen bombs exploded at the Patna railway station and in and around a ground where BJP leader Narendra Modi was to address a rally hours later.
The death occurred when the first of the otherwise low intensity blasts took place at around 9.30 a.m. at a toilet at the railway station's newly built platform 10, police said.
The railway station is located two-three kilometres from the Gandhi Maidan, the venue of the BJP prime ministerial candidate Modi's meeting. A second man was injured in the blast.
Two low-intensity bombs exploded at the Gandhi Maidan, injuring six people, and three more outside, police sources said.
Minister of State for Home Affairs C.P.N. Singh said in New Delhi that some 20 people were injured in the blasts.
Senior Superintendent of Police Manu Maharaj said police recovered two live bombs.
After the incident, police appealed to people, particularly those gathered for the Modi rally, not to touch suspicious objects.
Prime Minister Manmohan Singh condemned the serial blasts and called upon Chief Minister Nitish Kumar to speedily investigate the explosions and punish the perpetrators.
Manmohan Singh spoke to Nitish Kumar on telephone and urged people to maintain calm.
"The prime minister condemns the blasts which occurred at several places in Patna. He appeals to the people to maintain peace and calm," the Prime Minister Office's said on Twitter.
The chief minister later convened a high-level meeting to discuss the bomb attack.
In New Delhi, minister C.P.N. Singh said the bombings were "extremely unfortunate" and vowed to "get to the bottom of this".
He said the central government was in touch with the Bihar government, adding that the National Investigation Agency and National Security Guards had rushed their personnel to Patna.
Modi's well-attended rally passed off peacefully, however. In his speech, Modi made no reference to the blasts but towards the end asked the crowds to disperse "peacefully".