Omicron has started replacing Delta variant in the country in terms of the number of Covid-19 cases and 80 per cent of international travellers who tested positive have this new variant, official sources said on Friday.

However, a third of all the detected cases were mildly symptomatic, and the rest were asymptomatic, they said.

A total of 1,270 Omicron cases have been detected across 23 states and UTs so far, according to the Union health ministry data updated on Friday.

Noting a considerable decline in Covid testing, the Centre had on Thursday urged 19 states/UTs to ramp up testing "in a big way" to identify the positive cases promptly and restrict the spread of transmission in view of the increased transmissibility of Omicron variant, and the larger preponderance of asymptomatic cases.

Since, the first two cases of Omicron variant were announced in the country on December 2, the health ministry has been working in a mission mode and constantly guiding states on the measures to be undertaken to contain the spread of the infection.

Prime Minister Narendra Modi is also regularly holding meetings to review the status of Covid-19, Omicron and preparedness of health systems across the country, while Union Health Minister Manuskh Mandaviya reviews the ongoing situation with expert teams and senior officials daily.

He also takes updates on the buffer stocks of drugs and ventilators and oxygen availability.

The health ministry's war room is working 24x7 and analysing all trends and surges, and monitoring the nationwide situation.

The ministry has advised states and UTs to enhance testing, strengthen hospital preparedness, increase the pace and coverage of vaccination drive and ensure strict enforcement of restrictions to counter the spread of infection wherever necessary.

It also advised setting up containment zones and buffer zones as per extant SOPS, strengthening hospital-level preparedness and ensuring optimal utilisation of financial resources under ECRP-2.

Ninety per cent of India's eligible adult population has been administered the first dose of the coronavirus vaccine and 64.40 per cent people are now fully vaccinated.

Highlighting the vaccination coverage in other countries with highest cases and deaths, sources said the data shows vaccination reduces hospitalisation and death.