China's top environment watchdog disclosed violations of smog-easing measures as heavy air pollution in the north are set to persist.

The Ministry of Environmental Protection (MEP) punished over 500 enterprises and construction sites and 10,000 vehicles for breaching haze response plans.

The move came as 72 cities in the Beijing-Tianjin-Hebei region and Shaanxi Province have issued or maintained yellow or more severe smog alerts, MEP said.

China has a four-tier warning system for severe weather, with red being the most serious, followed by orange, yellow and blue.

When a high alert is in force, heavy polluting vehicles and trucks carrying construction waste are banned from roads and some manufacturing firms shall cut production.

Inspectors sent by the ministry have identified several metallurgy, agricultural chemicals and steel plants in the region which failed to follow the alert-triggered bans.

Government of heavy-industry Tangshan city, Hebei Province, is warned for failing to strictly abide by a truck-ban on its roads.

Meanwhile, an unlicensed quarry in the city was found to have continued operation even after one of its officials had been detained, MEP said, citing it as an example of foot-dragging over rectification orders.

The ministry has urged local governments to take prompt remedial actions and deal wrongdoings with severe punishment.

As of late January 2, China's national meteorological center has renewed orange smog alerts for large swathes of the northern region.

The smog is predicted to dissipate from the evening of January 8 with the arrival of a cold front, MEP said.

(Xinhua News Agency January 2, 2017)