Madrid on Thursday lifted an unprecedented ban on half of most private cars as pollution in the Spanish capital eased up.

A day earlier and for the first time in Spain, authorities decided to implement a measure already used in other cities abroad by ordering vehicles with even-number registration plates to drive on even-number days, and cars with odd-number plates on odd-number days.

The measure took effect on Thursday, but it was short-lived.

In a tweet, Madrid city hall said it had lifted the partial ban from Friday "given the improvement in NO2 (nitrogen dioxide) and (weather) forecasts."

The partial ban on cars is activated when levels of harmful NO2 in the atmosphere go above 200 microgrammes per cubic metre in at least two measuring stations for a specific period of time, and if the air is unlikely to clear imminently.

There are exceptions to the ban, such as for mopeds, hybrid cars, those carrying three people or more or used by disabled people.

Buses, taxis and emergency vehicles are also exempt.

But city hall said that some restrictions, such as a ban on parking in the city centre for non-residents, would continue as pollution levels had still not come down to satisfactory levels.

Still, Madrid stood Thursday at a moderate 70 on the international Air Quality Index that measures and combines five major air pollutants, one of which is nitrogen dioxide.

This compared to 140 in London and more than 300 in Delhi.