Singapore shares hit their highest in nearly five-and-a-half years, while Singapore Airlines was on course for its biggest daily drop in nearly 19 months after posting disappointing results.

The Straits Times Index rose nearly half a% to 3,457.07 points, its highest since the beginning of 2008, and the MSCI's broadest index of Asia-Pacific shares outside Japan inched down 0.2% .

Shares of Asia's second-biggest airline, SIA, fell as much as 4.4% to $10.95, its lowest in nearly three weeks, after the company reported weaker-than-expected full-year results and warned of a tough environment.

About 1.4 million shares of SIA changed hands, more than double of its 30-day average in trading volume.

"With the lacklustre results, continuing challenges ahead, and possible disappointment over the lack of a special dividend that some on the street had anticipated, we expect selling pressure on the counter, especially after it gained 8% since mid-April," said OCBC Investment Research in a note.

It downgraded SIA to "sell" with a fair value estimate of $10.00.