While the first blast took place at the train station at around 9:30 am, six successive explosions rocked Gandhi Maidan, where Modi later delivered an hour-long speech, within an hour.
Officials defused five other bombs as the National Investigation Agency (NIA) took charge of probing the incidents.
Even though Modi did not refer to the blasts in his speech, Bihar Chief Minister Nitish Kumar, who earlier this broke an alliance with the BJP over making his Gujarat counterpart the Prime Ministerial candidate, defended his administration.
At a press conference in the evening, the Kumar said that security arrangements were not inadequate and stressed that there were no intelligence alerts about the possibility of explosions.
He said "what happened today is the collective responsibility of all parties" and "a lesson not just for Bihar, but for all of India."
A man, who was allegedly caught running way from the train station where the first blast took place at 9:30 am, has confessed to planting the bombs, unconfirmed media reports said.
Two others have been also been reportedly caught in neighbouring Jharkhand state capital Ranchi with huge quantity of cash and explosives.
The Union Home Ministry meanwhile sought a report into the bomb attacks from the state government.
Minister of State for Home Affairs RPN Singh earlier in the day said National Investigation Agency (NIA) and National Security Guards (NSG) teams have been dispatched for Bihar.
"We have dispatched NSG,NIA teams to Patna. Sadly, Bihar government has confirmed to us that 5 people have been killed in the blasts. Appeal for calm at this time," RPN Singh tweeted.
Prime Minister Manmohan Singh condemned the blasts and spoke to Chief Minister Nitish Kumar over telephone and asked him to investigate the matter.
He urged the people of the state to maintain peace and calm.
"Prime Minister condemns the blasts which occurred at several places in Patna today. He appeals to the people to maintain peace and calm," the Prime Minister's Office (PMO) tweeted on Sunday.
"PM Dr Singh talks to Bihar Chief Minister Shri Nitish Kumar and asks him to speedily investigate the blasts, and punish the perpetrators," it said.
Meanwhile, Narendra Modi, who did not speak about the blasts while addressing the rally in Patna, later tweeted: "Blasts in Patna are deeply saddening and unfortunate. Condolences with families of deceased and prayers with injured. I appeal for peace and calm."
Senior BJP leader Sushma Swaraj condemned the blasts and said it was a result of 'gross' intelligence failure.
"I strongly condemn serial bomb blasts on the occasion of BJP rally in Patna. This is gross intelligence failure," Swaraj tweeted.
--IBNS (Posted on 28-10-2013)