More than 1,000 empty houses in Northampton should be used to help solve the national housing crisis, campaigners argue.
Action on Empty Homes said it is "exceptionally worrying" that more than half a million homes lie unused across England, while tens of thousands of families are living in temporary accommodation.
The campaign group's analysis of Ministry of Housing, Communities and Local Government figures show that 1,089 homes in Northampton were not being used as of October, up from 828 the year before.
Of these, 883 were long-term vacancies, unoccupied for at least six months, and 206 were second homes.
This means one in every 91 homes in Northampton were out of use – though this was below the average of one in 47 across England.
There were 268,000 long-term empty homes across the country – 19% more than the previous October, the biggest annual increase since current records began in 2004.
A further 263,000 are classed as second homes which are not in residential use long-term, and are not charged extra council tax when they are unused.
Action on Empty Homes said that the 531,000 properties without residents should instead offer "vitally needed housing" to the homeless.
Director Will McMahon said: “It can’t be right that in the last four years we have seen an escalating housing crisis while the number of long-term empty homes keeps rising.
"There are over 100,000 children languishing in overcrowded and temporary accommodation at a time when we know that overcrowded housing is being linked to the spread of the coronavirus and to higher mortality.
"It will be impossible to ‘build back better’ if we keep letting our housing crisis get worse."
Separate figures from MHCLG show there were 283 households in Northampton in temporary accommodation as of September, including 366 children.
They are among 59,400 families, including 120,600 children, in temporary accommodation across England.
Housing charity Shelter said it is frustrating to see so many empty properties, but a new generation of social homes is needed to solve the problem.
Chief executive Polly Neate said: "Tackling these empty homes is not an adequate alternative to building more genuinely affordable housing.
"We could fill every one of these properties and we still wouldn’t have solved the chronic housing shortage we face."
A further 400,000 vacant homes across England had been used within the last six months, including 1,515 in Northampton.
An MHCLG spokesman said: “We have given councils powers and strong incentives to tackle empty homes, including the power to increase council tax by up to 300% on these properties, and take over the management of homes that have been empty for a long period.
“They also receive the same New Homes Bonus for bringing an empty home back into use as for building a new one.”