Plans to create up to 90,000 new homes in the Thames Gateway have been criticised by The Campaign for the Protection of Rural England (CPRE).
A report by the CPRE says that green belt land will be destroyed if the current redevelopment plans go ahead.
It also claims that London's housing shortage problems can be solved by building only on brownfield sites.
The CPRE report says it backs the creation of new homes but is concerned about the loss of "fragile habitats".
The Thames Gateway is a 40-mile-wide area from east and south-east London to Kent and Essex.
The London part of the site is already earmarked for
60,000 new homes.
But Mayor of London Ken Livingstone says it could take at least 91,000 to meet London's long-term housing needs.
A blueprint shows 55 primary schools, six police stations and 19 health centres are needed for the new population.
Mr Livingstone said: "Nowhere else in the city offers a comparable opportunity to deliver new homes at the same time as delivering major improvements for existing residents."
But some environmental campaigners are worried about the fate of the green belt, poorer air quality and worse traffic.
And there have been some concerns about the possible effect on the flood plain of the Thames.
Proposals for a £385m six-lane bridge from Greenwich to Newham which aim to bring new investment to the area have been backed by Transport for London (TfL).