India is expected to send 5,00,000 doses of Covishield vaccine to Sri Lanka on Thursday.
It is learnt that the consignments are being sent to the island nation as a "gift" from India.
Prime Minister Narendra Modi had made a commitment to his Sri Lankan counterpart Mahinda Rajapaksa during a virtual summit in September last that India will provide all possible support to the island nation to minimise the health and economic impact of the coronavirus pandemic.
So far, India has sent consignments of coronavirus vaccines under grant assistance to Bhutan, Maldives, Nepal, Bangladesh, Myanmar, Mauritius and Seychelles.
Last week, India began commercial exports and sent two million doses each to Brazil and Morocco.
India is also sending coronavirus vaccines as commercial supplies to Saudi Arabia, South Africa, Bangladesh and Myanmar.
In a major announcement, India on January 19 said it would send COVID-19 vaccines under grant assistance to Bhutan, Maldives, Bangladesh, Nepal, Myanmar and Seychelles and supplies to Sri Lanka, Afghanistan and Mauritius will commence after confirmation of necessary regulatory clearances.
India is one of the world's biggest drugmakers, and an increasing number of countries have already approached it for procuring the coronavirus vaccines.
India has already rolled out a massive coronavirus vaccination drive under which two vaccines, Covishield and Covaxin, are being administered to frontline health workers across the country.
While Oxford-AstraZeneca's Covishield is being manufactured by the Serum Institute, Covaxin is being produced by Bharat Biotech.
India had earlier supplied hydroxychloroquine, Remdesivir and paracetamol tablets, as well as diagnostic kits, ventilators, masks, gloves and other medical supplies to a large number of countries to help them deal with the pandemic.