The environmental protection authority in Guangzhou, Guangdong province, is set to issue an emergency plan to tackle the city's recent bout of heavy smog.

Sources with the authority said on Monday that emergency measures, which include keeping 20 percent of the city's government vehicles off the road, are ready to be implemented.

Guangzhou, along with neighboring cities in the Pearl River Delta area, has been hit by prolonged smog since Jan 1, the authority said.