A deadly fire swept through a building at the site of the Serum Institute of India (SII) in the western Indian city of Pune on Thursday, but the world's largest vaccine maker said production of its much-needed COVID-19 vaccines won't be delayed.

CEO Adar Poonawalla reassures the fire, which left at least five people dead, will have no impact on the production of the Oxford-AstraZeneca vaccine named ChAdOx1 nCoV-19, but known locally as Covishield. He said vaccine production will continue "due to multiple production buildings that I had kept in reserve to deal with such contingencies."

Poonawalla said he was saddened by the five deaths.

"We have just received some distressing updates," he said on Twitter. "Upon further investigation, we have learned that there has unfortunately been some loss of life at the incident. We are deeply saddened and offer our deepest condolences to the family members of the departed."

The cause of the blaze at a production unit hasn't been determined, but Pune city mayor Murlidhar Mohol confirmed the five deaths. Rescue workers discovered five bodies in the burned-out building, which was under construction, after the blaze was brought under control.

As the world's largest vaccine maker by number of doses, SII produces 1.5 billion doses of different vaccines every year. The vaccines developed include the tuberculosis vaccine Tubervac (BCG), Poliovac for poliomyelitis, childhood vaccines and now COVID-19 vaccines.

SII will provide 100 million doses of a vaccine in India and other low and middle-income countries at around $3 per dose to support the goal of a low-priced vaccine championed by billionaire Bill Gates.

On Aug. 7, 2020, the Bill & Melinda Gates Medical Research Institute (Gates MRI) entered into partnership with SII to develop a vaccine that will be available to poorer countries for less than $3 a dose. The partnership will make available up to 100 million doses of a COVID-19 vaccine for rapid distribution to low- and middle-income countries.

SII also has an agreement with American vaccine firm Novavax for the development and commercialization of Novavax's NVX-CoV2373 COVID‑19 vaccine candidate in India and other low and middle-income countries.

It will also produce CDX-005, the nasally administered COVID-19 vaccine from British vaccine firm, Codagenix.

India began exporting vaccines on Wednesday. The first shipments went to Bhutan and the Maldives. Two million doses will later be sent to Bangladesh and one million to Nepal.

India has recorded the second-highest number of Covid-19 infections in the world after the United States. It has confirmed more than 10.6 million cases and almost 153,000 deaths since the pandemic began, based on data from Johns Hopkins University.