Blackpool Tower has been lit up with an SOS message as businesses in the town say they have had "mass cancellations" on an "unimaginable scale" since moving into tier three Covid-19 restrictions.
Over 1,000 traders have written an open letter to the prime minister asking him to save the resort's tourism industry.
Hotels and guesthouses, which are usually full during October half term, "lie virtually empty", they said.
The letter states urgent aid is needed or many businesses would shut.
Leader of Blackpool Council Lynn Williams said the speed at which the tourism economy had "unravelled" after the tier three move was "alarming".
She said it had become "totally apparent" that financial support put in place was "nowhere near enough" to support a tourism industry like Blackpool's.
The letter to the prime minister said the announcement about Lancashire being moved into the highest alert level, hours before it came into force, created "chaos and confusion" leading to "a collapse in consumer confidence".
The October half term holiday can account for up to 20% of total annual income for some businesses, it said, adding that the tourism industry was worth £1.6bn to Blackpool and supported 25,000 jobs.
The financial settlement for Lancashire was "nowhere near sufficient" and a package of aid was urgently needed, the letter warned.
Kate Shane, from Merlin Entertainments, which manages the tower, said it was "catastrophic" to "lose the most important two weeks of the year".
She said if the government does not put in place "bespoke measures" to help Blackpool's tourism businesses, it would "jeopardise years of investment in regeneration".
Claire Smith, president of holiday association Stay Blackpool, said following the move to tier three there were "cancellations on a scale that none of us in the hotel industry have ever experienced before".
Martin Long, chair of the Blackpool Business Leadership Group, said: "Tens of thousands of people are directly employed within the tourism sector, but there are many, many more who work in the supply chain and are almost wholly dependent on there being a thriving visitor economy."
The government has been contacted for a response.