The Polish city of Krakow, where high levels of air pollution have been reached in recent winters, on Tuesday offered free public transport to travelers in a bid to reduce the use of private vehicles, local authorities said on Radio Poland.

The city's government also called on residents to go outdoors as little as possible due to high pollution levels.

Poland has 33 of the 50 most polluted cities in Europe, with worryingly high levels of airborne particles, according to a report by the World Health Organization published in 2017.

Krakow, the second largest city in Poland, dates back to the seventh century and attracts visitors due to its history as a magnet for academic and artistic activity over hundreds of years.

Polish cities regularly exceed air pollution limits set by the European Union, mainly due to the use of low-quality coal in inefficient and outdated home heaters, and a lack of wind to blow the smog away.

According to forecasts, 90 percent of Krakow will in the coming days exceed concentrations of 150 milligrams of contaminant particles per cubic meter.

The EU's upper limit is set at 50 milligrams.

Last year the city government offered free transport and other incentives for 19 days in a bid to reduce pollution.