Sir Sadiq Khan has announced plans to "actively explore" building on some of London's green belt in a bid to resolve the capital's housing crisis.
The mayor of London says current rules prohibiting development on green belt land are "wrong, out-of-date and simply unsustainable", as as the demand for housing increases.
In a "radical step-change" in approach, planners will consider releasing some stretches of the land if conditions on affordable housing, energy efficiency, transport links and access to green spaces are met.
The London Conservatives said the idea was a "complete betrayal" of the mayor's previous pledges to protect the green belt.
Giving a speech in Greenwich, south-east London, Sir Sadiq blamed a rise in mortgage interest rates, Brexit and "spiraling construction costs" for contributing to London's housing crisis.
The Office for National Statistics (ONS) has said those who rent homes in the capital experienced a rise of 11% last year, while 183,000 Londoners are estimated to be living in temporary accommodation, such as hotels and hostels.
City Hall added that about 88,000 new homes are needed each year for at least the next decade to meet demand.
Housing crisis damage 'pervasive and profound'
"We have young professionals stuck in their childhood bedrooms for years on end, lifelong residents being priced out of their own neighbourhoods… primary schools closing because young families can't afford local properties," said the mayor.
"The damage the housing crisis causing is pervasive and profound."
He said he would with the government to speed up building projects on brownfield sites, but warned, "this alone will not be sufficient to meet our needs".
"City Hall's new position is to actively explore the release of parts of London's green belt for development."
He said a large quantity of green belt land in London was "low-quality", with only 13% of it being parkland accessible to the public.
"Given the quality of London's green belt and the extent of London's crisis, I believe the current position is wrong, out of date and simply unsustainable.
"Development in carefully chosen areas of the green belt, done in the right way would allow us to unlock hundreds of thousand of new homes."
The mayor also warned that he would intervene if councils did not speed up planning applications.
