China shares made tentative gains after officials announced fresh steps to rein in short selling, while commodities weakness spread to some Asian currencies, including the Malaysian ringgit.

The Shanghai Composite Index opened up 0.5% at 3630.51, and the smaller Shenzhen Composite Index rose 0.8% to 2069.21. The small-cap ChiNext board is up 1% to 2422.76.

Chinese regulators are continuing to roll out rescue measures to stem a 30% decline in equities since mid-June. Late Monday, the Shanghai and Shenzhen stock exchanges announced revised rules on short selling to curb high-frequency trading, according to statements published on their official websites.

Under new rules, short sellers must wait at least one day to cover their positions and pay back loans used to buy shares. Previously, investors could cover their positions within the same day.

Regulators said the earlier practice could "add to abnormal volatility of stock prices, and affect market stability," according to the statement.

The move comes as Chinese regulators have deepened scrutiny of automated trading. A total of 38 trading accounts on the Shanghai and Shenzhen Stock Exchange have been frozen as of Monday over trading irregularities, including one account managed by U.S.-based hedge fund firm Citadel Securities.

Meanwhile, a continued slide in commodities—from oil to gold and copper—has pressured some Asian currencies.

A slump in oil, which has fallen below $50 a barrel, stands to threaten Malaysia's oil-export revenues and deals another blow to the battered ringgit, already one of Asia's worst-performing currencies this year. The currency also has struggled amid a continuing investigation into the troubled state investment fund 1Malaysia Development Bhd., stoking worries over the nation's political stability.

The U.S. dollar traded as high as 3.8650 ringgit from 3.8498 late Monday in Asia. The currency fell as much as 0.9% against the U.S. dollar Monday, its biggest move in eight weeks, and is down 10.6% this year. Expectations of a U.S. rate increase later this year, which could incite investors to shift to less-risky assets, adds another layer of uncertainty.

Malaysia's exports, due Wednesday, likely contracted for the third consecutive month as a sluggish global economy and weak commodity prices weighed on demand. Exports are expected to fall 0.4% in June from the same month a year earlier, according to median forecast from a survey of nine economists by The Wall Street Journal.

Brent oil futures were down 0.8% to $49.89 a barrel in Asia trade, after data Monday showed a gauge of Chinese factory-floor activity slumped to a two-year low. A decline in the U.S. the Institute for Supply Management's manufacturing purchasing managers index added to pressure.

Gold prices were down 0.7% at 1083.18 an ounce in Asia trade, with the yellow metal hitting five-year lows in recent days amid a higher U.S. dollar and expectations of a U.S. rate increase.

Stock markets in the Asian region were roughly flat. The Nikkei Stock Average fell 0.2%, South Korea's Kospi was up 0.1% and the S&P ASX 200 was up 0.4%.

In Australia, the central bank is widely expected to keep its cash rate steady at a record low 2.0% in its policy meeting Tuesday, although the economic outlook remains clouded for policy makers. Some recent data has pointed to strength in hiring and business conditions, and consumer confidence has been rising. However, a protracted commodities slump has pressured Australia's resources-dependent economy. While the Australian dollar has fallen to six-year lows, a potential boon to exporters, a downturn in mining investment continues to hurt the broader economy and non-mining business investment remains weak.

Write to Chao Deng at Chao.Deng@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires