China has responded to reports of an indefinite ban on Australian coal imports, saying the move is to protect the interests of Chinese importers and the environment.

Key points: China says a ban on Australian coal is to protect Chinese importers and the environment

China says a ban on Australian coal is to protect Chinese importers and the environment Foreign Ministry spokesman said the block was "normal practice"

Foreign Ministry spokesman said the block was "normal practice" He warned against "baseless speculations" in the wake of a cyber attack on Parliament

Customs officers based at a key port in the north of China have reportedly stopped Australian coal imports, which sent the Australian dollar tumbling yesterday.

"China's customs assesses the safety and quality of imported coal, analyses possible risks, and conducts corresponding examination and inspection compliant with laws and regulations," Foreign Ministry spokesman Geng Shuang said.

"By doing so, it can better safeguard the legitimate rights and interests of Chinese importers and protect the environment."

The move appears political, with only Australian coal being targeted. Reuters said imports from Russia and Indonesia would not be affected.

When asked why Australian coal was targeted, he said the risk assessments followed regulations and inspection measures.

"I believe this is normal practice," Mr Geng said.

The spokesman also appeared to make light of the questioning by saying: "You were saying 'coal', not 'cow', right?", prompting laughter from the reporter.

The Dalian custom officers oversee imports through five harbours — Dalian, Bayuquan, Panjin, Dandong and Beiliang. Port authorities did not respond to calls for comment from the ABC.

Reserve Bank governor Philip Lowe has played down the threat to Australia's economy, telling MPs the exports involved are a relatively small proportion of Australia's coal exports.

"The amount of coal that is being blocked is the equivalent of two months' exports from Australia to China. It's entirely possible that if that cannot enter the Chinese market then it can go to other markets," he said.

"If it were to be the sign of a deterioration in the underlying political relationship between Australia and China that would be much more concerning."

A market research note from the National Australian Bank (NAB) said that Australia's trade to China through the Dalian port made up just 1.8 per cent of Australian coal exports.

Dr Lowe said he would not jump to the conclusion that it was a direct hit at Australia, saying it could be driven by "concerns about the environment in China and the profitability of the coal industry in China".

A ban on Australian coal sent the dollar tumbling. ( AAP: Dave Hunt )

'Baseless speculation' over cyber attack

When asked if the reported ban was linked to Huawei and the recent cyber attack on the Australian Parliament by a "sophisticated state actor", Mr Geng said cyberspace activities were "difficult to trace".

"One should present abundant evidence when investigating and determining the nature of a cyberspace activity instead of making baseless speculations and firing indiscriminate shots at others," he said.

"Cyber security should be upheld by all members of the international community as it is a global issue that concerns the common interests of all countries."

Mr Geng said China-Australia relations were solid.

"As we stressed many times before, a sound and stable China-Australia relationship serves the common interests of both countries and peoples," he said.

"China hopes Australia can work with us to advance bilateral relations on the basis of mutual respect, equality and mutual benefit."

China said the risk assessments were done to safeguard its interests and "protect the environment". ( ABC News: Brant Cumming )

Federal Treasurer Josh Frydenberg cautioned against labelling Australia's coal exporting difficulties with a "ban" and denied the move was a form of retribution over the Huawei scandal.

"I wouldn't jump to conclusions. The Australia-China trading relationship is exceptionally strong," he told RN Breakfast.

"They've in the past put in testing systems in place, and as [Trade Minister] Simon Birmingham has said, our ambassador will be making inquiries.

"Our exports to China will continue to be strong as they have been in the past."

He said Australia's coal exports were worth more than $60 billion and the industry creates 50,000 jobs.

Josh Frydenberg said China and Australia enjoyed strong trade relations. ( AAP: Mick Tsikas )

His comments echoed those made by Mr Birmingham yesterday, who urged caution.

"We can see these occasional interruptions to the smooth flow but that doesn't necessarily translate to some of the consequences that aspects of the media might seek to leap to," Mr Frydenberg said.

Earlier this week, BHP chief executive Andrew Mackenzie said delays for coal importers had doubled from 20 days to 45 days and that he didn't see the issue as political.



'Means and motive'

Suspicion quickly fell to China following the reports of the hack, and the communist state had "means and motive", according to Tom Uren, a senior analyst at the International Cyber Policy Centre.

"China has a record of just wide-ranging espionage and Australia is clearly a target for them," he said.

"There are a number of countries in the region who would like to know what Australia is up to and all to some extent would be interested in Australian politics — but almost all of them do not have the capabilities to do something like this."

He added the "usual suspects" for such attacks were North Korea, Russia and China.

He said China historically hadn't covered its digital tracks well, but that appeared to have changed.

He added that a dramatic drop in Australian exports could send an important domestic message.

"It can also look like good PR, in a warped Communist Party way, to say they at are stopping Australian exports," he said.