Most shares in Asia were back in the red Wednesday with Australia slipping below breaking even for the year amid a renewed fall in oil prices and a nearly 10% plunge in shares of Anglo-Australian BHP Billiton Ltd.

The S&P/ASX 200 was down 1.2%, giving back some of its gains from yesterday when Australia's central bank cut interest rates. The benchmark, heavy on energy shares, is now close to flat for the year, after breaking into positive territory for the first time this year yesterday.

Heavy decliners Wednesday included BHP Billiton, which tumbled 9.6% in Sydney. That followed Brazilian federal prosecutors filing a civil lawsuit Tuesday that demands mining companies—BHP Billiton, Brazil's Vale SA, and their joint-venture Samarco Mineraç ã o—shell out up to $43.55 billion for cleanup and remediation related to a catastrophic dam failure last year.

Losses elsewhere in Asia included a 1.3% decline in the Hang Seng Index, also weighed down by the energy sector. South Korea's Kospi was down 0.6%. The Shanghai Composite Index slipped 0.4%.

"The street is back again to focusing on low global growth and looking at the crude price as a barometer here," said Gavin Parry, managing director at Parry International Trading Ltd.

The weakness reflects how shaky the region's rally has been since mid-February, as global growth fears simmer in the background. Meanwhile, Japan's stock market, which tumbled for two sessions before closing for a three-day holiday, reopens Friday. That market has been especially volatile, as investors try to gauge the Bank of Japan, which last Thursday left monetary policy unchanged.

Pressuring Japanese shares is the yen, which has been at its strongest levels since October 2014. A strong currency at home generally hurts exporting companies by making their goods less competitive and eroding their repatriated earnings.

"Increasing [currency] volatility resulting from central bank policies is transmitting waves of uncertainty through global markets," said Margaret Yang, market strategist with CMC Markets. "A stronger yen will probably continue to blacken the outlook for Japanese equity markets."

During Asian overnight hours, U.S. crude oil prices declined, bringing its losses in three sessions to more than 5%. That sent U.S. stock indexes lower.

By early Wednesday in Asia, the fall was also weighing here—energy shares fell almost 4% in Australia and 2.9% in Hong Kong. Shares of Rio Tinto Ltd. and Fortescue Metals Group Ltd. were 6% and 4.2% lower, respectively.

In Australia, shares are close to joining benchmarks in Korea and a number of Southeast Asian countries in positive territory for the year, although steep declines remain in the region, with Shanghai stocks still off 15% since the beginning of the year.

Ric Spooner, CMC Markets chief market strategist, said that "traders are becoming concerned about the possibility that the next volatile market swing, in this case downward, may not be too far away."

Losses in BHP in Sydney follow a 5% plunge for the firm's London listing overnight.

In currencies, the Australian dollar, which reached its weakest level against the U.S. dollar in more than a month after the central bank's rate cut, was last rebounding by 0.3% in early Asian trading.

Paul Kiernan contributed to this article.

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

(END) Dow Jones Newswires

May 04, 2016 00:15 ET (04:15 GMT)