Hundreds of demonstrators have marched through central Hong Kong to protest against air pollution.

Some wore medical masks, others dyed their hair blue to demonstrate their support for clear skies.

March organisers said pollution levels in some districts of Hong Kong exceeded safety guidelines and they called on the administration to give a higher priority to cleaning up the air.

The BBC Hong Kong correspondent says diesel-fuelled cars and buses are thought to be key contributors to the apparent worsening of air quality and environmental activists want moves to control their emisssions speeded up.

Hong Kong officials have defended their record on the issue.