BEIJING, May 18-- Polluters need to watch out for an eye in the sky as drones have helped the Ministry of Environmental Protection (MEP) detect factories flouting environmental laws in one of China's most polluted provinces.

The ministry dispatched drones in March to Handan City in north China's Hebei Province, where they uncovered violations including excessive emissions and inadequate waste processing, the ministry said on Monday.

Several companies missed deadlines for putting anti-pollution facilities into operation, and others do not have any waste processing facilities, the ministry said, quoting monitoring results from the drones.

They are equipped with infrared devices which can allow them to work during the night.

The drones found a polyphenyl ether factory that was under construction without passing necessary environmental assessment and a stone factory pouring polluted water into surrounding rivers.

Local authorities have fined these violators, according to the MEP.

Ministry official Zou Shoumin said it will continue to use drones, which he called a "secret weapon", for random pollution inspections in more polluted areas.

The MEP also said that checks of construction sites, roads and coal storage yards in 52 cities since March had found 88 violations of laws designed to limit smog. The law-breaking included excessive emissions and faking of pollution data. East China's Jiangsu Province was found to have the most violations.