Television channels showed thick clouds of grey smoke billowing from the site in Pune in western India.

The Serum Institute is producing millions of doses of the Covishield coronavirus vaccine developed by AstraZeneca and Oxford University.

“It is not going to affect production of the Covid-19 vaccine,” a source at the Serum Institute told AFP, adding that the blaze was at a new plant under construction.

An official at the local fire station told AFP that six or seven firetrucks had reached the site.

“We have no other information… on the extent of the fire or whether anyone is trapped,” the official said.

In January, Indian regulators approved two vaccines — Covishield, produced by the Serum Institute, and Covaxin, made by local firm Bharat Biotech.

India began one of the world’s biggest vaccine rollouts on Saturday, aiming to vaccinate 300 million people by July with both Covishield and Covaxin.

Many other countries are relying on the Serum Institute to supply them with the vaccine.

India exported its first batch on Wednesday — to Bhutan and the Maldives — followed by two million doses to Bangladesh and a million to Nepal.

The country plans to offer 20 million doses to its South Asian neighbours, with Latin America, Africa and Central Asia next in line.

Serum Institute, the world’s biggest vaccine maker by volume, also plans to supply 200 million doses to Covax, a World Health Organization-backed effort to procure and distribute inoculations to poor countries.

AFP