By Chao Deng 

Chinese shares finished lower Thursday, swinging wildly in the last hour of trading, and extending a pattern of intraday volatility that started with mid-June's selloff.

The Shanghai Composite ended down 2.2% at 3705.77, after snapping a three-day losing streak on Wednesday. The index traded as high as 1.5% and as low as 2.7%, or within a 4.2% range. That compares with a range of 4.9% on Tuesday and 9.1% on Monday, when the index suffered its worst daily percentage decline in more than eight years.

The volatile trading follow authorities' recent signals to continue supporting the market and steps to investigate sharp declines.

The smaller Shenzhen Composite ended 3.2% lower at 2128.16.

Hong Kong's Hang Seng Index was down 0.4%, while a gauge of Chinese companies listed in the city was down 2.7%.

Earlier this week, China's stock regulator said it would continue to support the market, though authorities don't disclose the pace of buying, or the total amount that they have bought up in stocks.

Officials also are investigating possible coordinated dumping of shares, after earlier this month restricting senior executives and shareholders who own more than a 5% stake from selling for six months.

The securities watchdog has investigated a total of 27 listed firms over share sales in violation of rules in July, according to a report by state-run People's Daily.

On Wednesday, the securities regulator said a listed arm of China's state-owned aerospace and defense company and its two largest shareholders are under investigation for potential violation of stock-selling rules. Shares of AVIC Heibao Co. were up 5.4%.

The crackdowns have made some investors uneasy, with an increasingly unpredictable pace of regulatory changes.

"Investors are in a limbo due to uncertainty of regulation. The regulator sets the rules and changes the rules without any sign," said Zhang Xin, analyst at Guotai Junan Securities.

The selling this month appears to have helped flush out leveraged bets in the market. Vincent Chan, an analyst at Credit Suisse, said that financing for buying stocks by informal lending channels, as tracked by one major trading system, likely dropped sharply since mid-July. Authorities have been clamping down on margin financing--the borrowing of money by brokerages and unofficial lenders to investors--in an attempt to stamp out speculative activity. Margin loans spur stocks to rise and fall quickly.

Still "the direction may be irreversible," Mr. Chan wrote in a note Thursday. "Informal activities will turn back to offline and be underground, only to serve big individual clients as they were before."

Asian shares elsewhere mostly rallied after the Federal Reserve offered few clues on plans to raise interest rates for the first time in nearly a decade. Its easy-money policy, mirrored by central banks around the world, has helped fuel stock gains since the global financial crisis, and a delay in raising rates could give stocks more steam.

The Nikkei Stock Average rose 1%, helped by a weaker yen. The Japanese currency was last at Yen124.15 compared with a close of Yen123.94 in New York.

Australia's S&P ASX 200 was up 0.8% and South Korea's Kospi was off 0.9%.

In South Korea, shares of Samsung Electronics Co. were down 3.8% after the firm logged its fifth-straight year-over-year drop in profit. Sales for the company's flagship Galaxy S6 smartphone fell short of market expectations and hurt profit.

In commodities, an unexpected decline in U.S. crude-oil supplies and production led to a recovery in oil prices. Brent crude, the global benchmark, was up 16 cents at $53.55 a barrel in Asian trade. Prices have slumped this month on renewed fears about a global glut and faltering demand from China, one of the world's biggest consumers.

Gold prices rose sharply after the Federal Reserve's statement, but quickly gave up gains. Gold rallied as high as $1,100.90 a troy ounce in aftermarket trading Wednesday as is currently at $1,084.50 in Asia.

Gold had sank to five-year lows in recent weeks amid expectations for a rate increase, which could incite investors to move to higher-yielding assets.

Yifan Xie contributed to this article.

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