People protect themselves from the pollution in Beijing's downtown Guomao area during heavy smog on Friday. ZOU HONG/CHINA DAILY

Northern regions of the country will confront more frequent and stronger smog this winter due to the impact of the La Nina phenomena, a senior air pollution control official warned.

La Nina is a periodic cooling of the surface of the equatorial Pacific Ocean, which causes abnormal weather patterns.

Beijing has experienced four rounds of smog since October, and neighboring cities like Tianjin and those in Hebei province have issued emergency response alerts.

"La Nina will bring challenges for governments to control smog during the heating season, but the peak this year will not be as high as last year," said Liu Bingjiang, head of the Ministry of Environmental Protection's atmospheric environment department.

In November and December, many cities including Beijing, and Harbin in Heilongjiang province, saw air quality index readings off the chart.

Liu said the Beijing-Tianjin-Hebei region has taken tough measures to reduce emissions. For example, over 500,000 households in the region have changed their energy consumption from coal to gas or electricity, which is forecast to cut the emission of sulfur dioxide and dust by 40,000 metric tons.

But governments are urged to fully implement the restrictive measures, especially on smoggy days, said Tian Wei-yong, head of environmental monitoring in the ministry.

The ministry's inspection teams, which have been in eight smoggy cities since Wednesday, have exposed many companies that were discharging pollutants against government restrictions, Tian said.

"For the polluters, it's more than just receiving heavy fines," he said. "Those who falsify monitoring data will face severe punishments from judicial organs."

Chen Jining, minister of environmental protection, said the revised laws have helped to deter polluters and reduce pollution.

Cao Yin contributed to this story.