London (CNN Business) London is the first city in the world to implement a 24-hour, seven day a week Ultra Low Emission Zone, inside which vehicles will have to meet tough emissions standards or face a charge.

Monday's introduction of the zone, known as the ULEZ, aims to reduce toxic air pollution and protect public health, according to a press release from the office of Sadiq Khan, mayor of London.

Vehicles are responsible for around half of harmful nitrogen oxide air emissions in the British capital, contributing to a toxic air health crisis that increases the risk of asthma, cancer and dementia as well as causing thousands of premature deaths every year, the release says.

"This is a landmark day for our city. Our toxic air is an invisible killer responsible for one of the biggest national health emergencies of our generation," Khan said in the statement.

"The ULEZ is the centerpiece of our plans to clean up London's air -- the boldest plans of any city on the planet, and the eyes of the world are on us."

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