For a number of years, cities around the world have been facing increasingly global and aggressive speculation in their property markets – from speculators who see housing in our cities as an asset from which to profit, rather than homes for the people we represent.

In many cases, speculators take decisions from thousands of miles away. Yet for us their impact on the life and soul of our cities is very close to home. Our city centres risk being hollowed out as vibrant communities are displaced, local shops are closed, and the cost of housing rises exorbitantly.

Cities are not simply a collection of buildings, streets and squares. They are also the sum of their people

Our community groups and local government, as the part of civic life closest to local people and the most sensitive to their everyday problems, have often been the first to warn of the risks that these practices bring with them regarding the very survival of our cities.

For city leaders to be able to tackle this problem, they urgently need greater resources and powers both to increase their stocks of social-rented and other genuinely affordable housing and to strengthen tenants’ rights.

Cities are not simply a collection of buildings, streets and squares. They are also the sum of their people. They are the ones who help create social ties, build communities and evolve into the places where we are so proud to live.

That is why we are determined to change the way that housing works in the cities we represent. We are building more social-rented and other genuinely affordable homes, doing all we can to strengthen the rights of tenants, and clamping down on bad practices of developers and landlords wherever we are able to.

But we face a complex problem and one that operates at a global level. We still lack the powers and resources that would allow us properly to regulate the housing market, to protect tenants’ rights to remain in their homes, and to make homelessness and rough sleeping things of the past.

Meanwhile, our national governments, by contrast seem happy to abandon cities to their fate. We are calling on them to address this problem by providing the resources and powers we need to build all the social-rented and other genuinely affordable homes we need, and to make sure tenants are protected in their homes. Global cities are facing a housing emergency. If we do not ensure that the purpose of housing is, first and foremost, to provide homes for our citizens rather than speculative assets, we will struggle to build liveable cities for our citizens for generations to come.

Mayors and local governments of world cities are working together to share knowledge and find solutions to the housing crisis. It is our duty to do everything possible to all citizens improve their lives and participate fully in our communities. We will only succeed if we can make sure everyone in our cities has access to a decent, secure and affordable home.

• Sadiq Khan is the mayor of London and Ada Colau is the mayor of Barcelona