China Eastern Airlines (CEA) finally admitted on Monday that pilots on 21 flights deliberately turned their aircraft round in flight, affecting more than 1,000 passengers in Yunnan Province.

Chinese media has labeled the pilots' actions an 'unofficial strike' over a call for better management and treatment.

From March 31 to April 1, 21 flights returned to their departure points in Yunnan Province, in southwestern China, and CEA originally said the incidents were due to poor weather. However flights with other airlines flying the same routes landed on schedule during the same period.

The China Meteorological Administration (CMA) said the weather condition was fine for the flight landing on March 31.

The airline's response sparked suspicion and anger among passengers who pressed for more convincing reasons.

The airline has suspended the pilots, and further probing is underway, said an announcement on the company's website.

Heads of the airline's Yunnan branch were also suspended from their posts after the headquarters sent the company's deputy general manager Li Yangmin to act as the regional head, according to the statement.

By the afternoon of April 1, the airport resumed operation and no passengers remained stranded.

The company said on April 5 that pilots involved in "flight returns" would be penalized if they were found to have acted on grievances rather than "poor weather." CEA added that passengers would be compensated.

The Civil Aviation Administration of China (CAAC) sent a team to investigate four days after the incident.