Hainan Airlines, China's fourth biggest carrier, said Tuesday its net profit almost quadrupled last year, buoyed by a booming domestic industry and the stronger Chinese currency.

Net income reached 651.4 million yuan ($91.7 million) or 0.18 yuan per share, up from 166.8 million yuan or 0.06 yuan in 2006, the Haikou-based airline said in a statement to the Shanghai Stock Exchange.

Operating revenue rose 6.1 percent from a year earlier to 13.6 billion yuan last year, it said.

The airline reaped 11.3 billion yuan from passenger transport last year, after carrying 14.5 million passengers, up 0.7 percent. But cargo transport volume declined 0.5 percent to 197,800 tons.

China, the world's second largest air transporter after the United States, reported an improved profitability of its civil aviation industry last year as transport capacity expanded, market demand rose and the domestic currency appreciated, the statement said.

Chinese airlines carried 185 million passengers last year, up 15.9 percent, while cargo volume surged 13.3 percent to 3.96 million tons, according to government estimates.

Hainan Airlines planned to raise passenger numbers by 16 percent to 16.75 million in 2008.

"Considerable appreciation of the yuan led to a sharp shrinkage of US dollar-denominated debts that the company paid back in 2007," it said.

China moved its currency, the yuan, away from a pegged exchange rate to the US dollar in July 2005 and has allowed it to appreciate by about 14 percent since then.

Hainan Airlines added eight aircraft to its fleet last year, bringing the total to 66, including 58 Boeing 737s. The airline will invest 9.8 billion yuan this year in transport capacity expansion.

Another 17 new aircraft will join in this year, including the purchase of 10 Boeing 737-800s for about 3.5 billion yuan.