Singapore Airlines, the world's second-biggest carrier by market value, posted on Wednesday a 73 percent surge in quarterly net profit on strong passenger sales but warned it could be hit by a slowing world economy and rising fuel costs.

The airline, 51 percent-owned by state investment agency Temasek Holdings, said the business landscape remains challenging although advanced bookings on its flights were still holding up.

Slowing economic growth sparked by tight credit markets and increasing volatility in financial markets cast a cloud of uncertainty over the strong revenue environment, the company said in a statement. The carrier reported second-quarter net profit of S$508 million ($350 million), up from S$293 million from a year ago.

It carried 9.4 million passengers in the first half of its financial year, pushing its operating profit in the April-September period to S$982 million, up 82 percent from a year ago.

Singapore Airlines raised its fuel surcharges last week by 6-9 percent, citing jet fuel prices that rose 43 percent this year to a record $104.40 a barrel on Tuesday.

It started commercial flights of the double-decker Airbus A380, the world's biggest jumbo jet, last week with a Singapore-Sydney service.

But it may face competition between Singapore and Kuala Lumpur, monopolised currently by Malaysian Airline System (MAS) and Singapore Airlines, after the countries said last week they aimed to liberalise the route.

MAS said on Wednesday the government decision to open the lucrative route to competition ahead of time will hurt earnings.

Shares in Singapore Airline -- valued at S$17 billion and ranked behind only Air China's $28.6 billion -- are up nearly 12 percent this year, but lag the broader Singapore market's 26 percent rise and gains of 18 percent by regional rivals Cathay Pacific Airwaysand Qantas.