While Modi was not in the vicinity of any of the blasts in Bihar on Sunday, they were a reminder of India's bloody political history, that includes the assassination of former Prime Minister Rajiv Gandhi at an election rally in 1991. (Agencies)
The Hindu nationalist Modi is seen as a target of Islamist militants who hold him responsible for riots in 2002, during his first term as Chief Minister of Gujarat state, in which at least 1,000 people, most of them Muslims, were killed.
Sunday's violence was a sign of heightened tensions in the early stages of a campaign that has already coincided with an uptick in communal clashes between Hindus and Muslims.
India is due to elect a new government by May 2014 in a contest pitting the political outsider Modi, favoured by business, against the ruling Congress party's Rahul Gandhi, the scion of a political dynasty stretching back more than 60 years.
Modi denies any role in the 2002 riots or bias against minority Muslims. He has gathered momentum in recent weeks and opinion polls suggest his BJP could win enough seats to form the next government in a coalition.
He used Sunday's rally to call for unity between poor people of both faiths and pundits predicted he could enjoy a ratings boost because of sympathy after the attack.
The BJP accused the Bihar government of failing to secure the ground where tens of thousands of supporters gathered and demanded that authorities overseeing the election do more to stop attacks.
One party leader, Subramanian Swamy, said that he wrote to Prime Minister Manmohan Singh demanding Modi be given secret-service-style security.
"I think he should have special protection. It appears to me that the huge crowds that turn out to see Narendra Modi upset those who have much to lose from him gaining power,” Swamy said.
Modi is already given a large security detail made up of a mixture of ‘Black Cat’ commandos and Gujarat Police.
At least six crude bombs exploded near the rally ground in Patna, after an initial blast at its railway station. Police recovered four unexploded devices inside the ground, none close to the stage where Modi spoke.
Television images showed flames shooting several metres into the air when one of the devices exploded. Despite the bloodshed, Modi spoke for about an hour after rally organizers decided cancelling the event would risk triggering a stampede.
Modi's likely main challenger in the next election, Rahul Gandhi, the son of Rajiv Gandhi, said last week that he too was worried about assassination. Rahul's grandmother, Prime Minister India Gandhi, was assassinated in 1984.
Police said that they had arrested a suspect after the railway station blast and said he had given details of the operation. They said they found a piece of paper on him listing seven other suspects.
Police also said that they had found a suspicious substance at the suspect's residence and were testing to see if it was an explosive.
A senior police officer in Patna said that they were investigating the possibility that a home-grown Islamist militant group, the Indian Mujahideen, was behind the attack, but the suspect has not admitted any connection to the group.
India holds the Indian Mujahideen responsible for the deaths of hundreds of people in numerous attacks over the last eight years. The organization, which has links to Pakistan-based militants, often uses multiple small bombs in attacks.
Tensions between Hindu and Muslim communities tend to rise before elections, often stirred for political gain. Rioting killed close to 50 people in India's most populous state a few weeks ago.
The BJP first rose to national prominence during the destruction by Hindus of the Babri Masjid mosque in 1992, an event that sparked rioting that killed some 2,000 people.
Modi's conciliatory tone on Sunday stood in contrast to the violence around him, and the attacks could help him win over some undecided voters.
"This will benefit Modi by polarizing things even more. People will see that an attempt was made to stop him and that will win him sympathy," said Neerja Chowdhury, political commentator and former political editor of the Indian Express.
While Modi was not in the vicinity of any of the blasts in Bihar on Sunday, they were a reminder of India's bloody political history, that includes the assassination of former Prime Minister Rajiv Gandhi at an election rally in 1991.