Almost 5,000 acres of land have been lost from the green belt in the past year, official figures show.
The area of designated green belt in England was around 2,000 hectares (4,940 acres) less than the previous year - a reduction of around 0.1%, the statistics from the Department for Communities and Local Government (DCLG) reveal.
The reduction, which is the biggest annual change for five years, is down to eleven local authorities adopting new plans for their area which removed land from the green belt, often to allow for development.
Of the 11 councils, Rushcliffe in Nottinghamshire saw the biggest reduction in green belt land with boundary changes removing 670 hectares (1,650 acres) from the designation, while Newcastle-upon-Tyne had the biggest percentage reduction, losing 9% of its green belt.
Since 1997, there has been an increase of 32,000 hectares (79,000 acres) in green belt land to protect against urban sprawl, after green belt re-designated as being part of the New Forest National Park has been taken into account, officials said.
A DCLG spokesman said: "Only in very special circumstances can building on the Green Belt be justified, and we have put in place strong protections to prevent inappropriate development in the countryside through the national planning policy framework.
"We are encouraging new development on brownfield land and expect to see planning permissions for homes in place on 90% of suitable brownfield sites by 2020."