Indian Prime Minister Narendra Modi has appointed a yoga minister in a major revamp of his government after storming to power in May, in a bid to promote the ancient practice.

Yoga-loving Modi beefed up his right-wing government on Sunday by appointing 21 new ministers, with the aim of speeding up reforms to revive the faltering economy.

Among the portfolios designated late Sunday was that of AAYUSH, whose minister will be charged with promoting the traditional medicines and practices of Ayurveda, yoga, naturopathy, Unani, Siddha and homeopathy.

Hindu nationalist Modi, a vegetarian who practises yoga daily, asked the United Nations in September to consider an international yoga day.

During his visit to the United States, Modi also discussed the ancient Indian discipline with President Barack Obama during their dinner at the White House.

"Congratulations to all colleagues who have taken oath today. Looking forward to working with them to accelerate India's development journey," Modi said in a tweet late Sunday.

Modi added four new ministers to his cabinet, and 17 junior ministers for a 66-member strong government including the premier.

AAYUSH was previously part of the health minister's responsibility, but has become a separate portfolio after Sunday's reshuffle, with former tourism minister Shripad Yesso Naik taking charge.

Among other changes, suave regional leader Manohar Parrikar was handed the defence ministry charged with modernising the country's ageing armed forces.

Parrikar's appointment will ease the burden on Arun Jaitley, who had been juggling both the defence and finance ministries since the government took office in May, while battling ill-health.

Jaitley also takes information and broadcasting under the revamp, but will be mostly free to focus on steering through difficult reforms pledged during the election campaign to revive the faltering economy.

Parrikar, with a reputation for clean government during his time as chief minister of tourism state Goa, will be expected to speed-up long-delayed defence orders and overhaul the country's Soviet-era military hardware.

A series of corruption scandals under the previous Congress government had brought defence procurement to a near standstill.

Although it has introduced some reforms, the government has so far steered clear of "big bang" initiatives that economists say are needed to boost investment and manufacturing.

Jayant Sinha, the Harvard-educated son of a former finance minister, was named junior minister for finance, underlining Modi's priority to boost business and attract foreign investment.

Railways was handed over to Suresh Prabhu, a veteran leader of the Hindu hardline regional Shiv Sena party who switched allegiance to the ruling Bharatiya Janata Party (BJP) just before Sunday's swearing-in ceremony.