Southeast Asian stock markets ended down in thin trade on Thursday as investors stayed away ahead of holidays, with all markets posting losses in 2015 except for Vietnam.

Singapore's key Straits Times Index dipped 0.1 percent in mixed trade, with losses in most big caps offsetting gains in several blue chips.

The index, Southeast Asia's worst performer this year, posted a 14.34 percent drop in 2015. The stock market traded for half a day on Thursday and will be shut on Friday for the New Year holiday.

Kuala Lumpur's composite index stood nearly flat, edging down 0.04 percent, with volume hitting a seven-week low in thin trade. The market ended 2015 with a 3.9 percent loss, its second year in a row.

Vietnam eked out a 6.12 percent gain in 2015, the slightest rise in four years. However, the country this year is the sole gainer in Southeast Asia.

The region's markets finished mostly down for the year, reflecting a difficult 2015 for its mainly export-dependent economies, with the Thomson Reuters index of Southeast Asian bourses down 19 percent.

Singapore and Thailand saw the biggest slumps while the Philippines, Indonesia and Malaysia also reported losses. Only Vietnam, the smallest of the six bourses, finished the year in positive territory, a fourth consecutive year of gains.

Malaysia and Vietnam are closed on Friday.

Stock markets in Indonesia and Thailand are closed on Thursday and Friday. The Philippines will be closed on Friday.