Thirty European cities pledged Thursday to slash their greenhouse gas emissions by 40 percent as French President Francois Hollande called on them to back historic UN climate talks.

"Your role... is to show... that it is possible to live and live well in large urban areas and under a model that allows us to react to the demands of global warming," Hollande told city leaders.

The 30 towns -- including Paris, Rome and Madrid -- vowed in a declaration to cut by 40 percent their emissions by 2030, which is the target laid out by the European Union.

Under the pledge, the cities will work together to invest public money in green technology and services.

Paris will host a major UN conference in December that aims to finalise and ink an historic climate pact to curb global warming.

"I ask you to mobilise to the fullest extent in order to bring as much pressure to bear as necessary," to ensure an agreement is reached, Hollande said.

"It's March and we know that time is running out," he added, warning that the danger would be to think "we have as much time as we want to reach an agreement."

"Large European cities must be pioneers in terms of bulk purchase of equipment, standards on traffic and support for low-emission creating businesses (and) green space," Hollande said.

The office of Paris Mayor Anne Hidalgo said cities can work together to buy electric and hybrid cars, electricity from renewable sources as well as trash compactors.

"To convince oneself that the climate challenge is indeed a local challenge, one need only remember that by 2050 cities will house two thirds of the world's population and emit 70 percent of carbon emissions," Hidalgo told reporters.

Also present at Thursday's meeting in Paris were mayors from Athens, Bucharest, Geneva, Lisbon, Sofia, Stockholm, Vienna and Warsaw.