China's listed coal companies turned major profits last year, reversing previous deep losses, because of rising coal prices according to the latest estimates - but one leading industry expert has warned of unsustainably high prices.

According to an estimate by the National Development and Reform Commission, total profits by the country's designated large coal companies with annual turnovers of at least 20 million yuan ($2.9 million) were 95 billion yuan in 2016.

One major producer - China National Coal Group Corp - has estimated its net profits at 1.8-2.2 billion yuan in 2016, compared with losses of 2.5 billion yuan the previous year.