And while the Chinese moves might cause some disruption for companies exporting cheaper coal through the Port of Newcastle, spot prices for high-energy thermal coal have risen by almost $US7 ($9.80) a tonne, or 14 per cent, since late August.

Cheaper coal often destined for China has risen by about half as much to $US40 ($56) a tonne.

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Although Canberra has played down the significance of the Chinese moves, BHP confirmed after last week's annual general meeting that some of its Chinese customers had asked to defer shipments, based on "verbal" instructions from Beijing that are being treated across the industry as factual.

The Hong Kong-based South China Morning Post described the move last week as a Chinese "ban" on imports of Australian coal.

Some China-watchers have said the supposed push-back over Australia's call for an investigation into the Chinese origins of COVID-19 was simply a convenient way for the country to back its own domestic industry against cheaper imports.

This view is backed by those who point out that China has done nothing to curb imports of Australian iron ore, with the troubled Brazilian industry the only real competitor to the Australian product at the heart of the massive Chinese steel industry.

The Post quoted former Australia China Business Council chief Helen Sawczak as saying: "China is trying to manage several factors including an uncompetitive domestic industry, a domestic stockpile, supply quotas (and a) recent pledge to be carbon neutral by 2060.

"Unlike iron ore, there are several countries which China can import coal from, including Australia."

Time-series graphs from the Australian Bureau of Statistics and the Reserve Bank of Australia show China was a minor Australian customer until 2007-08, when its imports of thermal coal for electricity generation, and coking coal and iron ore for steelmaking, began a rapid rise that has only slowed in the past few years.

The Australian export coal industry was built on sales to Japan, which valued stable, long-term relationships and was prepared to pay higher prices for energy security.

The figures in the table above, taken from the latest ABS monthly summary of Australian coal exports, shows that while China is an important customer for various types of coal, it is perhaps not as dominant as it is sometimes portrayed.

Australian coal faced delay-causing restrictions at some Chinese ports last year, and this latest round of concern surfaced in the first half of the year, when the Chinese government reportedly told power stations not to buy Australian product - a move that would have been most felt through the Port of Newcastle, which ships most of Australia's export thermal coal.

Coal loader operator Port Waratah Coal Services said that last year, 47 per cent of its exports went to Japan, followed by 18 per cent to China, 15 per cent to Taiwan and 12 per cent to South Korea.

The industry says thermal coal has decades yet as a major commodity.

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