Indian vaccine maker Bharat Biotech is seeking international manufacturing partners as it targets a billion doses of its COVID-19 vaccine each year, the company said on Sunday.

COVAXIN, the company's home-grown COVID-19 vaccine approved for emergency use in India, is one of two shots driving the country's massive vaccination programme.

But Bharat Biotech has struggled to boost output, missing supply commitments to the Indian government, which is also relying on a version of the AstraZeneca vaccine produced by the Serum Institute of India and Russia's Sputnik V vaccine.

On Sunday, the company rolled out the first batch of COVAXIN shots from a facility in Ankleshwar in western India that has the capacity to produce more than 10 million doses per month.

Bharat Biotech said it was exploring opportunities with its international partners who have expertise in commercial-scale manufacturing of inactivated viral vaccines.

"We want to ensure that Bharat Biotech can ably meet the demand for COVAXIN such that individuals across the country, and the globe, have access to the vaccine," chairman and managing director Krishna Ella said in a statement.

Last month, Health Minister Mansukh Mandaviya told parliament that Bharat Biotech would supply 25 million doses in July and 35 million in August, less than half what the government had initially expected.