More than five million people have fallen into a "fragile" financial position owing to the coronavirus crisis, with young working adults among the hardest hit.
People from black, Asian and minority ethnic backgrounds were also more seriously affected than others, the Financial Conduct Authority (FCA) said.
The regulator said "the pain is not being shared equally".
An estimated 14.2 million people are vulnerable to a financial shock.
The regulator's Financial Lives survey is a benchmark for the state of the nation's finances.
A total of 16,000 people were interviewed in February last year, with another 22,000 spoken to in October, after the pandemic struck.
As a result, it gives a snapshot of the first six months of restrictions caused by the coronavirus crisis.
The findings suggest that a quarter of the UK adult population now have low financial resilience. That means they have debts that are hard to manage, low savings, and are vulnerable to a financial shock such as a large, unexpected bill.
The number of people who fell into that category rose by 5.1 million between February and October.
Many people have cut back on essentials, around a fifth expect to borrow from family and friends, and one in 10 plan to use a food bank.
"While there are some positives in the data, many of the findings are worrying," said Nisha Arora, director of consumer and retail Policy at the FCA.
"The pain is not being shared equally with a higher than average proportion of younger and BAME adults becoming vulnerable since March. It is likely the picture will have got worse since we conducted the survey."