Government-backed loans worth £330 billion will be made available to support businesses through the coronavirus crisis.
Chancellor Rishi Sunak said the unprecedented package, equivalent to 15% of GDP, could go further if demand is greater, and vowed to do "whatever it takes" to help the economy.
The Chancellor, speaking at a press conference inside 10 Downing Street, also said he was extending the business rates holiday to all businesses in the hospitality sector and funding grants of up to £25,000 for smaller businesses.
And Mr Sunak said that for those in financial difficulty due to coronavirus, mortgage lenders will offer a three-month mortgage holiday.
He unveiled the measures after the Government's chief scientific adviser said around 55,000 people in the UK now have Covid-19, as the NHS moved to cancel all non-emergency surgery and 71 people are now known to have died.
Sir Patrick Vallance told MPs it is hoped the death toll can be kept to under 20,000 as he told of the huge amount of strain the health service will be under from Covid-19.