At least 12 people have died of swine flu in India, health ministry officials have confirmed.

The outbreak has affected 129 people since the beginning of March. Many are still in hospital. The western state of Maharashtra is worst hit, with six deaths in and around Pune, the state's second-largest city after Mumbai.

Five people have died in the northwestern state of Rajasthan and one more in the southern state of Andhra Pradesh.

Five cases of swine flu have also been confirmed in the southwestern state of Karnataka, but no deaths were reported.

Swine flu killed more than 450 Indians when it first emerged in May 2009 and has killed more than 1,800 since.

Health secretary PK Pradhan has told people not to panic during the latest outbreak.

"The health ministry is monitoring the situation and there is no cause for worry. The states where cases had been reported have been advised to step up surveillance to control the further spread of the virus," Pradhan told the Press Trust of India.

Officials said it was not immediately clear why there was a sudden outbreak of the disease.

"Last year globally, swine flu was at an ebb," National Institute of Virology director AC Mishra told The Indian Express daily.

"While short spurts are being recorded in other countries this year, it could well be a short spell where the virus will surge and then die down," he said.

The swine flu (H1N1) virus first emerged in Mexico in April 2009.