Reports say Australian coal exports are still being delayed on their way to China.

Coal exports are taking almost twice the normal amount of time to unload, and Australia has sought an explanation for the delays.

Trade Minister Simon Birmingham says he has accepted assurances from Chinese authorities that the blowout in wait times was not specific to Australia.

He said China has started to back its own coal industry, leading to a more protectionist stance, and is also limiting steel production.

Reports say China has also increased its quarantine checks for environmental reasons.

“If that's the case we have nothing to fear because Australia's coal is amongst the best in the world in terms of the environmental standards that come when it is used,” Senator Birmingham told the ABC.

“We're trying to understand all of those different moving parts and watching very closely what's happening at each of the ports in terms of the speed of processing times.”