Underlining the highly transmissible nature of Omicron and the preponderance of asymptomatic cases, the Centre has urged nine states and union territories to ramp up COVID-19 testing to ensure that infected people do not spread the virus to others.

In a letter to Tamil Nadu, Punjab, Odisha, Uttar Pradesh, Uttarakhand, Mizoram, Meghalaya, Jammu and Kashmir and Bihar, Additional Secretary of Union Health Ministry Arti Ahuja pointed out a considerable decline in COVID-19 testing amid rising cases and positivity rate and said it is a "cause of concern".

In the absence of sufficient testing, it is rather impossible to determine the true level of infection spread in the community, Ahuja said in her letter dated January 5.

"With the increased detection of the Variant of Concern (VOC), Omicron, and a majority of countries seeing multiple surges in cases despite high levels of vaccination, there is a need for continued vigil and efforts to prevent any deterioration of the COVID-19 scenario.

"Keeping in mind the unpredictable and highly transmissible behaviour of Omicron and the larger preponderance of asymptomatic cases, ramping up testing in the initial days itself will help to ensure that the infected individual does not spread the virus to others," she said.

It has been observed that there has been a considerable decline in COVID-19 testing in these states and union territories amid rising cases and positivity, which is a cause of concern, Ahuja said.

She advised them to review and ensure availability of sufficient stock of testing reagents and kits etc., and regular arrangement of testing facilities, consumables, and logistics.

India on Thursday saw the biggest single-day jump of 495 Omicron cases, taking the total number of infections of the new variant of coronavirus to 2,630, according to Union health ministry data.