* Aust shipments down 20.4 pct in Jan-Aug, Indonesia down 43 pct
* Weak demand, price signals deterring imports
* North Korean shipments continue to rise (Adds detail, analyst quotes)
BEIJING, Sept 21 (Reuters) - China imported 6.39 million tonnes of coal from its top supplier Australia in August, down 12.8 percent on the year, with the country's cost advantages eroded by declining domestic prices, data from the country's customs authority showed on Monday.
Australian miners normally benefit from a surge in demand in the summer as power plants in southern regions source cheaper coal from overseas, but oversupply has eroded the gap between domestic and overseas coal prices this year.
Analysts said overall imports are likely to remain under pressure for the rest of the year, with orders hit not only by weak demand but also by the devaluation of China's currency, which has further eroded the price advantages of foreign coal.
Australian imports were down 21.8 percent compared to July. Over the first eight months, the total reached 48.64 million tonnes, down 20.4 percent compared to the same period of 2014.
Total August imports, excluding lower-grade lignite, reached 13.48 million tonnes, down 11.6 percent compared to August 2014, with demand faltering as a result of China's economic slowdown and its campaign to boost the use of cleaner fuels.
Late last year, China announced it would impose restrictions on the import and utilisation of low-grade coals, and Australia has complained that its cargoes have been unfairly rejected at Chinese ports as a result of new quality standards. ID:nL3N0ZI2U9
But Australia's higher grades and lower costs have meant that it has fared better than rivals like Indonesia. China's second biggest supplier of imported coal saw deliveries fall 18 percent in August to 2.38 million tonnes, and is down 43 percent over the whole of the year.
"With prices currently so low, importers will certainly choose higher-quality coal," said Zhu Limin, coal analyst with Shanghai Securities.
"Normally, coal demand will increase over the winter, but whatever happens, China is not expected to slash imports from countries that produce high-quality coal, including Australia," he said.
Shipments to China from North Korea surged 41.8 percent in August to 1.82 million tonnes, and are up 33 percent over the whole of the year. Zhu said the surge might be driven by politics rather than the market.
Benchmark Newcastle coal prices GCLNWCPFBMc2 stood at $55.75 a tonne at last week's close, down more than 9 percent since the start of the year. Prices at the Chinese port of Qinhuangdao SH-QHA-TRMCOAL stood at 400 yuan ($62.82) a tonne, down 23.8 percent.
($1 = 6.3669 Chinese yuan)