Seven people have been detained for polluting the air of the host city of this year's G20 summit, east China's Hangzhou.

Hangzhou has focused on cleaning up the emissions of more than 30 businesses from mainly heavy industries, including plating, printing and smelting, according to Hangzhou police on Monday.

Seven bosses from four companies which failed to use mandatory pollution control facilities were held for seven or eight days, the bureau said.

The Hangzhou environmental protection bureau also closed down several unlicensed enterprises.

"Hangzhou police works with environmental protection departments to punish polluters," said local police officer Xia Guoliang.

Hangzhou, a popular tourist city and capital of Zhejiang Province, will host this year's G20 summit in September.