Australian shares closed flat on Wednesday as the combination of soft local and Chinese data as well as the festering Sino-US tariff war offset sharp gains for miners.

The S&P/ASX 200 index ended flat at 6,543.70, having gained 1.6 per cent on Tuesday.

A downturn in Hong Kong stocks, as thousands of demonstrators protested against a proposed extradition bill, added to a cautious mood as investors fretted over more pressing concerns around global growth and an escalating US-China trade war.

President Donald Trump said on Tuesday he was holding up a trade deal with China and had no interest in moving ahead unless Beijing agrees to four or five "major points" which he did not specify.

Financials snapped five straight sessions of gains and declined 0.7 per cent. Among the "Big Four" banks, top lenders Commonwealth Bank of Australia and Westpac Banking Corp lost 1.3 per cent and 0.9 per cent, respectively.

"It is common trade for international investors to buy into the high yielding finance sector when they buy into the Australian economy, so the pressure especially on banks suggests some international nervousness about the outlook for Australian market," said Michael McCarthy, chief market strategist at CMC Markets.

Adding to the pressure on the broad market, a private survey on Wednesday showed a measure of Australian consumer confidence dipped in June due to a run of disappointing indicators. Data showing cooling factory-gate inflation in China, Australia's major export market, also checked sentiment.

Elsewhere, drug maker CSL Ltd and medical devices maker Cochlear each fell about 2.2 per cent, weighing on the healthcare index.

The mining index advanced 2.5 per cent to a more than two month closing high as copper and iron ore prices rose.

China's iron ore futures extended their surge to record highs on Wednesday, boosted by concerns over tight supply after production disruptions at leading iron ore miners in Australia and Brazil.

Global miner BHP Group firmed 2.7 per cent and peer Rio Tinto added 1.9 per cent.

Fortescue Metals Group closed up 6.3 per cent. The world's no.4 iron ore miner's stock has more than doubled in value this year.

China's funding support for major investment and infrastructure projects is also seen as a boon to Australia, which is a major supplier of raw materials to the Asian giant.

New Zealand's benchmark S&P/NZX 50 index ended up 0.65 per cent or 65.99 points to 10,205.14.

Synlait Milk gained 4.9 per cent and was the best performer on the index, while Air New Zealand added 2.9 per cent.