BEIJING (Reuters) - Air pollution across 74 major Chinese cities worsened in July compared to last year, according to government data released on Tuesday, showing that the government is having trouble shaking its smog problem.

The 74 cities struggled with pollution on 26.9 percent of the days in July, up from 19.5 percent a year ago, data on the Ministry of Environmental Protection website said.

The air was worst in northern China, where Beijing, Tianjin and seven cities in Hebei province made the list of the 10 worst cities. Air pollution was judged high on 57.4 percent of the days in July, up from 51.4 percent last year.

Air pollution has figured high on the government's agenda since a choking smog dubbed the "airpocalypse" engulfed key Chinese cities in January 2013, leading Premier Li Keqiang to announce a "war on pollution" in March this year.

Data from Greenpeace, which monitors air quality reports from 190 cities nationwide, showed last month that PM2.5, a measurement of tiny particles in the air, had dropped 6 percent in January-June, compared with the same six months in 2013.

But Tuesday's government data showed that coal-reliant China is not making much of a dent in pollution levels despite closing down thousands of heavy-polluting facilities across the nation.

The number of high-pollution days in eastern and southern parts of the nation was less than half those in the north, although still growing, the data showed.

In the Yangtze River delta, Shanghai and 24 other cities faced high pollution levels on 25.1 percent of July days, up from 14.2 percent in the same month last year.

In nine cities in the southern Pearl River delta, pollution levels soared on 18.1 percent of days, compared to only 6.8 percent in July the year before.

Officials continue to introduce new policies and legislation to deal with the problem.

The Shanghai municipal government last month increased its maximum penalties fivefold for companies breaching environmental regulations.

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It also removed a law saying polluters could only be fined once, meaning the government can now impose new fines every day until companies comply with the law.

The move was in line with China's new environmental protection law, which aims to strengthen officials' abilities to implement environmental policies.

(Reporting by Stian Reklev; Additional reporting by Kathy Chen; Editing by Tom Hogue)