Urban windmills and solar panels on house roofs form part of Amsterdam's plans to cut carbon dioxide emissions by 40 percent by 2025, officials of the Dutch capital said Thursday.

Announcing the city's ambition to become a world exporter of renewable energy technology, mayor Job Cohen said it would strive to ensure a fifth of all energy consumed was "green" in 17 years' time.

"The competition between cities is fierce. I am sure that those cities who don't start work on renewable energy now will be out of the running within a few years."

Cohen was speaking at the start of a three-day conference entitled "Renewable Amsterdam" attended by public and private sector representatives.

He said energy used by the city government must be "climatically neutral" by 2015 -- which means it should either come from renewable sources or must have been compensated for through greening projects.

And by 2025, the city must have cut its CO2 emissions by 40 percent from 1990 levels, the major said.

A study commissioned by the city has found that it was possible to make 240,000 out of every 380,000 Amsterdam homes dependent on renewable energy by 2025.

"It is a big challenge," Cohen said. Currently only 5.7 percent of the city's energy (double the national average) came from renewable sources.

To bypass the obstacle of erecting windmills in confined areas and fix solar panels to steep-angled roofs, the municipality would rely on investment and creativity by the business community, said the mayor.