The blaze at the Serum Institute of India (SII) in the western city of Pune was brought under control on Thursday though the cause is still under investigation, according to Murlidhar Mohol, the city's mayor.

Four people were rescued from the six-floor building but five others died, Mohol said.

In December, the company said it was producing 50 to 60 million doses of Covishield per month, with production to be scaled up to 100 million doses in January or February.

A family business started by Poonawalla's father 50 years ago to bring cheaper vaccines to the masses, the Serum Institute of India is aiming to produce hundreds of millions of coronavirus vaccines for not only India, but also other developing countries.

In a tweet, Poonawalla said that despite a "few floors being destroyed," production of the Covishield vaccine would not be affected.

"I would like to reassure all governments and the public that there would be no loss of COVISHIELD production due to multiple production buildings that I had kept in reserve to deal with such contingencies," he said.