Indian Prime Minister Narendra Modi told officials on Saturday to review plans to ease travel restrictions as concerns rise over the new Omicron variant of COVID-19.

The world's second-worst affected country by the pandemic had only Friday decided to resume international passenger flights from countries deemed "at risk" of the coronavirus, while ordering tightened border screening.

But after the World Health Organization (WHO) declared the new variant to be "of concern", Modi "highlighted the need for monitoring all international arrivals, their testing as per guidelines, with a specific focus on countries identified 'at risk'," the government said in a statement after he met with officials to review the COVID-19 and vaccination situation.

The WHO said Omicron, initially detected in South Africa, may spread more quickly than other forms.

This week, India posted the smallest rise in new cases in one and a half years, due to increased vaccinations and antibodies in a large section of its population from previous infections.

The nation's daily caseload has halved since September. It reported 8,318 new cases in the last 24 hours.

But the new variant, with a spike protein dramatically different from the one existing coronavirus that vaccines are based on, has raised global alarms and frightened financial markets.

Modi said people must be more cautious and take proper precautions, such as wearing masks and social distancing.

He "spoke about the need to be proactive in light of the new variant," the statement said.

"He directed that intensive containment and active surveillance should continue in clusters reporting higher cases and required technical support be provided to states which are reporting higher cases presently."

Modi told officials to accelerate second-dose coverage, it said.