Architects have come up with designs for "Heathrow City" - a 190,000-home town that would spring up if the west London airport closes.

Supported by London Mayor Boris Johnson who backs a Thames Estuary airport to replace Heathrow, the redevelopment of Heathrow could potentially support 90,000 new jobs and add £7.5 billion to the UK economy.

Designs, from three firms of architects, include proposals for new park land, scientific research centres and a factory for modular housing units to make it easier for people to build their own homes.

Commissioned by Transport for London (TfL), the designs are:

:: Hawkins\Brown - This is the one that includes the factory-for-homes plan. Online customisation would allow Londoners to order homes to their own specifications as is common in a number of European countries, where 'self-build' is a popular way of creating new homes.

:: Rick Mather Architects - Their proposal would see the Heathrow site evolve to become a new hub city by working with the existing structure and using the terminals as generators to development. The former runways would define the structure of the city and connect 10 distinct local centres.

Developers would look to create a research, technology and manufacturing hub while a wide range of new housing types would also include 21st century re-interpretations of successful London models of individual houses, terraces, mansion blocks and communal squares.

:: Maccreanor Lavington - Their vision for Heathrow City aims to develop a fully functioning city within the metropolis, characterised by a rich mix of ecology, culture, employment and liveability. Existing buildings would be used to establish fresh development and new forestation is laid down.

A technology campus would be built to the east of the current site and new housing would be influenced by emerging trends that might include self-build, community-led development, temporary housing, a development corporation and developer-led housing delivery. The former Terminal 2 building would be renovated to become a civic centre and retail hub that would form the heart of the new community.

Mr Johnson said: "The demand for new homes and jobs in the capital is such that we must be ready to start redeveloping Heathrow the moment it moves to its new site. And the sooner we start planning the better.

"We asked our architects to be as creative as possible and these designs illustrate strikingly different visions of a Heathrow of the future."

He went on: "However the key point is that all these scenarios would potentially create some of the many thousands of new jobs and homes this city will require given London is expected to increase in size by a fifth within the next 15 years.

"How we deal with that is something we need to be planning for and debating right now. Those discussions must not be delayed."

The Thames Estuary airport plan - dubbed "Boris Island" is currently being considered by the Whitehall-appointed Airports Commission although recent reports prepared for the commission have cast doubt on the estuary scheme's feasibility.

The commission is due to make a decision this autumn on whether the estuary plan joins Heathrow and Gatwick runway schemes on the commission's shortlist.

A final decision on just where runway capacity should be increased will be made by the commission in summer 2015.