BEIJING, Feb. 6-- Chinese police solved more than 4,500 pollution crimes and arrested 8,400-plus suspects last year, six times the figure in 2013, according to the Ministry of Public Security.

Still, such crimes are likely to continue even after a suspect has been arrested, senior ministry official Hua Jingfeng said while unveiling the data at a press conference on Friday.

In addition to high recurrence, difficulties in collecting and authenticating evidence, as well as law enforcement obstruction from local officials make environmental crimes particularly troublesome, he said.

"Many chemical plants and mining companies that illegally discharge wastes are high-profit projects backed by local governments... Shutdown will result in financial losses and workers losing jobs. So local powers usually turn a blind eye to their environmental violations, and will even disrupt police efforts," Hua said.

Hua said some companies and individuals have a weak sense of the law, adopting various unlawful measures to reduce costs and escape supervision.

Environmental crimes uncovered included discharging waste via hidden pipes, altering equipment data on paper, only using waste processing facilities in the presence of inspectors and discharging waste to adjacent jurisdictions to avoid local scrutiny, Hua said, without revealing specific cases.

Meanwhile, Hua said China has a very limited number of eligible environmental data authentication institutes, which play a crucial role in determining environmental crimes. "

"With evidence in hand, our police usually don't know who to give it to," he said.

Police are determined to crack down on environmental violations and will strengthen cooperation with other departments, he said.