China is set to limit the operations of North Korean airline Air Koryo after one of its planes made an emergency landing in northeastern China last month.

The plane, Air Koryo Flight 151, heading from Pyongyang was heading to Beijing on July 22. However, the airline was forced to divert its route and landed in Shenyang after smoke appeared in the cabin.

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Investigations carried out by Air Koryo found that the smoke was caused by burning in an audio speaker found under a luggage rack, according to The Wall Street Journal, citing the Civil Aviation Administration of China (CAAC) on Wednesday.

The CAAC said the situation was classified as a "serious incident" and warranted punishment in the form of demerit points and "corresponding measures to limit operations," the statement said. No other specific details were given.

The Air Koryo aircraft, which was a Russia-built Tupolev 204, landed safely, and all passengers and crew aboard were unharmed.

"The North Korean airline would likely be a very resource-deprived airline, operating a number of older airplanes. And often, that older equipment is difficult to maintain. By international standards it would not be a great airline," Greg Waldron told BBC.

Now, Chinese aviation regulators are demanding that Air Koryo improves its training and maintenance including in-flight contingencies like engine-fire warnings, cabin depressurization, and air-traffic control communication.

Air Koryo is currently flying passengers from Pyongyang to three Chinese destinations (Beijing, Shanghai, and Shenyang) and the eastern Russian city of Vladivostok.

Tagschina, Air Koryo, emergency landing, North Korea airlines