Geneva, Dec 29 : The overall risk associated with the Omicron variant remains 'very high' which could cause widespread disruption to health systems and other critical services, the World Health Organisation (WHO) has warned. In its weekly epidemiological update, the WHO said on Tuesday that "The overall risk related to the new variant of concern Omicron remains very high". "Consistent evidence shows that the Omicron variant has a growth advantage over the Delta variant with a doubling time of two to three days," read the update. The warning comes as the new Omicron variant in the US has driven daily Covid-19 new cases to a record high of over 510,000. It is the highest single-day increase of cases since the onset of the pandemic in the country, according to the latest data from Johns Hopkins University. The Omicron variant, first identified late November in southern Africa, has sent infections soaring to levels not seen since last winter, bringing the total number of US coronavirus cases to more than 52.9 million, with more than 819,000 deaths. According to Catherine Smallwood, Covid Incident Manager with WHO Europe, Omicron's growth "will still result in large numbers of hospitalisations, particularly amongst unvaccinated groups, and cause widespread disruption to health systems and other critical services". Major cities in the US, including New York, have scaled down or cancelled New Year's Eve events for a second consecutive year. The Omicron variant caused more than 50 per cent of infections in the Netherlands over the past week, replacing Delta as the dominant variant, the National Institute for Public Health and the Environment (RIVM) has announced. Germany introduced tighter restrictions nationwide for vaccinated and recovered people in a bid to slow the spread of the Omicron coronavirus variant. Covid-19 has continued to ravage Europe, causing fear, stress and even despair across the board. In the last 24 hours, India registered 9,195 fresh Covid-19 cases, a significant spike from the previous day's figure of 6,358, and 302 deaths, the Union Ministry of Health and Family Welfare said on Wednesday. Meanwhile, airlines continue to cut flights as rising numbers of staff are infected by the Omicron coronavirus variant and bad winter weather disrupts parts of the US. As of Tuesday, 2,182 flights set to depart in the day have been cancelled, and the cancellations have amounted to about 13,000 since Friday morning, according to figures from the flight-tracking website FlightAware. /IANS