Chancellor Rishi Sunak has set out a £1bn fund to help businesses hit by the rise in Covid cases, including the leisure and hospitality sector.
Hospitality businesses like pubs and restaurants will be able to apply for cash grants of up to £6,000 per premises.
The government would also help some firms with the cost of sick pay for Covid-related absences, Mr Sunak said.
And he announced an extra £30m to help theatres and museums.
Many hospitality and leisure firms have been hit by a collapse in bookings and reduced footfall due to people's fears over the spread of the Omicron variant.
Mr Sunak said the new support was "generous" and recognised the situation facing businesses in the run-up to Christmas.
Some industry figures have welcomed what they described as "unprecedented" support, but others said the measures do not go far enough.
Businesses other than hospitality and leisure can apply for some of the funding.
However, the chancellor would not be drawn on whether more help would come should further restrictions be announced, as ministers come under pressure to tackle the rapid rise of Omicron.
Tough new rules have been brought in in Scotland, with a limit on the number of people allowed to attend large events and Edinburgh's Hogmanay street party being cancelled.
Another 90,629 new Covid cases were reported across the UK on Tuesday - slightly down on the all-time highs announced last week.
The announcement on Tuesday means:
Restaurants, bars, cinemas and theatres can apply for a grant of up to £6,000 for each of their premises. The Treasury is setting aside £683m for these grants and it will be provided under existing council-run schemes
Other struggling businesses outside leisure and hospitality can apply to local councils for a different grant under the Additional Restrictions Grant, which has been topped up with £102m
The Statutory Sick Pay Rebate Scheme is being reintroduced, meaning business with fewer than 250 employees can claim money to cover sick pay for employees who are affected by Covid
An extra £30m for arts organisations through the existing Culture Recovery Fund.
Asked if more support would be offered, the chancellor said he would "always respond proportionately and appropriately to the situation we face".
But he added that he thought the new measures announced were comparable to the grants that were on offer when businesses were fully closed earlier this year.
The UK's devolved administrations are also receiving £154m of funding to cover all three schemes, with around £80m for Scotland, £50m for Wales and £25m for Northern Ireland. This money is part of a fund announced earlier this week.
Challenged on whether he could rule out any more restrictions before the new year, Mr Sunak said he understood people's frustrations but the UK faced a very uncertain situation over Omicron.
He echoed the prime minister's comments on Monday, saying ministers were keeping the situation under review and monitoring the data "day-by-day, hour by hour" but ruling nothing out.
However, Labour's shadow Treasury minister Pat McFadden described Mr Sunak's announcement as "a holding package from a government caught in a holding position".
Mr McFadden said the support was "welcome" but that it should have been announced last week when MPs voted to pass the government's Plan B measures.