China's state environmental watchdog has urged local environmental departments to issue smog alerts and report information on heavy air pollution in a timely manner.

The departments should publicize such information via local broadcasting, television, Internet, newspaper and social media, according to a circular issued by the Ministry of Environmental Protection.

The document came as environmental authorities in some areas had failed to issue air pollution warnings and report pollution in an active and timely fashion, the circular said.

It further criticized them for slow emergency responses and failure to act on public concerns, saying this has discredited environmental protection departments.

They are also told to report air pollution information to government officials in order to provide a reference for decisions on whether to launch an emergency plan.

The circular added that press conferences should be arranged if necessary to release information on heavy air pollution and put forward protective measures and suggestions.

Days of lingering smog covering large parts of China forced school closures and flight cancellations earlier this month.