The number of tip-offs from the public about environmental violations has decreased by 23 percent in the first half of the year compared with the same period last year, the Environmental Protection Ministry said on Tuesday.

From January to June, the ministry's hotline "12369" received 696 phone calls, almost 60 percent of which related to the chemical, metallurgical and non-metallic mineral processing industries.

Echoing the distribution of the three industries in China, almost 40 percent of the cases came from four provinces – Henan, Shandong, Jiangsu and Hebei.

More than 80 percent of the tip-offs were about airborne pollution, an increase of 8.4 percent compared with the same period last year. Complaints about water pollution, noise pollution and solid waste pollution fell.

The ministry said 80 percent of those named in the tip-offs were found to have violated environmental laws and regulations, but no problems were found as a result of the other complaints.

Environmental departments at all levels have dealt with some 400 cases, and measures taken include setting a deadline to solve the problem, halting production, imposing fines and closing down factories.

"There are three major reasons for these problems – poor planning where industrial zones are located in residential areas, production starting before residents have moved away, and companies failing to act after receiving several warnings," said a ministry-level environmental official who asked not to be named.

He said approval for new projects would be withheld in cities or provinces where enterprises repeatedly violated environmental laws.

The new Environmental Protection Law, to be implemented on Jan 1, 2015, will give environmental departments stronger powers.