"I assure that I will leave no stone unturned in working for a BJP victory in the 2014 elections," Mr Modi said in a statement after being nominated.

"I seek the blessings of the people in our efforts to free our nation of the turbulent times we are going through."

Critics say his candidacy will shift the debate from the alleged scams and inefficiencies of the ruling Congress to Mr Modi's controversial persona, the BBC's Vineet Khare, in Delhi, reports.

But supporters see him as a strong figure who can lead the BJP to power, after it lost the last two parliamentary elections, our correspondent says.

A brilliant speaker, Mr Modi was chosen in June to lead the BJP's election campaign for next year. Some senior party leaders including former deputy prime minister L K Advani opposed his appointment.

However, Mr Modi has massive support both within the party as well as among India's middle classes and business community, who see him as a charismatic leader who has turned Gujarat into an economic powerhouse.

As a result, he was re-elected twice as the state's chief minister.

Mr Modi also enjoys strong backing from senior leaders in the right-wing Hindu organisation the Rashtriya Swayamsevak Sangh (RSS).

The RSS, founded in the 1920s with a clear objective to make India a Hindu nation, functions as an ideological fountainhead to a host of hardline Hindu groups - including Mr Modi's BJP, with which it has close ties.

The RSS has a particularly strong base in Gujarat, and Mr Modi's links were seen as a strength the organisation could tap into when he joined the state unit of the BJP in the 1980s.

Ability for secrecy

Mr Modi has a formidable reputation as a party organiser, along with an ability for secrecy, which comes from years of training as an RSS "pracharak" or propagandist, analysts say.

Although Mr Modi escaped censure in the 2001 Gujarat riots, his close aide, Maya Kodnani, was convicted last year and sent to jail for 28 years.

The rioting began after 60 Hindu pilgrims died in a train fire blamed on Muslims in the town of Godhra.

Ms Kodnani was not a minister at the time of the riots, but was appointed junior minister for women and child development by Mr Modi in 2007.

His critics accused him of "rewarding her with the ministership" for her role in the riots.

Mr Modi himself has never expressed any remorse or offered any apologies for the riots, and many Muslims displaced by the violence continue to live in ghettos near Ahmedabad, Gujarat's largest city and commercial capital.