PARIS, June 26 (Xinhua) -- Paris police on Wednesday decided to extend traffic restriction for another 24 hours as air quality has not improved amid the heatwave.

In a Twitter message, the prefecture said "only vehicles with clean car stickers 0, 1 and 2 class will be able to circulate on Thursday from 05:30 local time (03:30 GMT) to midnight."

That means 4.7 million motorists have been told to leave their cars at home on Thursday, or 60 percent of registered vehicles in Ile-de-France, according to local media.

On Wednesday, the most polluting cars are prevented from entering Paris after week-long heatwave has worsened air pollution.

Authorities also ordered to cut speed limits by 20 km per hour in Paris and Ile-de-France, while vehicles weighing over 3.5 tonnes should bypass the city centre and nearby surroundings completely.

They said 150 checkpoints have been set to implement the measure in the capital and the suburbs. Offenders risk to be fined up to 135 euros (about 153.47 dollars).