London's first low-emission bus zone has been launched as part of efforts to tackle "toxic air" in the capital.

One of the capital's most polluted areas, Putney High Street, is the first place getting the new initiative, with 145 buses on seven scheduled routes serviced by cleaner buses to cut emissions of nitrogen oxides, which harm health.

Only buses that meet the toughest emissions standards will be allowed to run within the Putney low-emission bus zone, which runs from Putney Station to Putney Bridge Road.

There will also be measures giving buses priority on the high street to keep delays to a minimum and reduce unnecessary pollution caused by sitting in traffic.

Putney High Street is the first of 12 low-emission bus zones planned for the capital, with a route in Brixton set to start later this year.

London will also see the phasing out of diesel-only buses, as they cause more pollution, and a commitment to purchase only hybrid or zero-emission double-decker buses from 2018.

Launching the new zone, London Mayor Sadiq Khan said: "London's toxic air is an outrage and I promised to make cleaning it up one of my top priorities.

"Today, I'm delivering on that pledge by introducing our first ever low-emission bus zone.

"I have asked TfL (Transport for London) to remove the oldest, dirtiest buses from our streets and this new route, along with the 11 others we'll be introducing, will make a big difference to the pollution caused by our public transport system.

"I now need other cities around the world to work with me to demand cleaner bus technology so we can phase out diesel buses altogether."

He also repeated a call to Government for a national diesel scrappage fund to help get the most polluting vehicles off the road and for powers to tackle other sources of air pollution.