BANGKOK (REUTERS) - Thailand's exports fell more than expected in December and contracted much more in 2015 than in the previous two years, showing how the trade-reliant economy continues to struggle amid weak global demand.

Persistently poor exports and domestic demand have added to the challenges the ruling junta faces moving South-east Asia's second-largest economy forward after seizing power to end political unrest 20 months ago.

Exports, worth about two-thirds of GDP, fell 8.73 per cent in December from a year earlier, the Commerce Ministry said on Tuesday (Jan 26). A Reuters poll projected a 7.2 per cent drop.

The fall was the 12th consecutive one and the biggest for any month since November 2011, when severe flooding forced thousands of factories to shut.

In 2015, exports fell for the third straight year. The annual drop was 5.78 per cent, the biggest in six years, compared with falls of less than 0.5 per cent in 2013 and 2014.

Preventing a bigger 2015 tumble was the key auto industry, as exports of cars and car-parts rose 4.3 per cent.

Despite the poor 2015 results, the Commerce Ministry is maintaining a target of 5 per cent export growth this year.

"Exports could be positive in Q1 due to a low base last year and if oil prices don't fall further," said Mr Somkiat Triratpan, a ministry official.

But the Bank of Thailand forecasts zero growth this year. Governor Veerathai Santiprabhob told Reuters last week "we expect quantity to be expanding a bit but that will be offset by declines in export prices".

Thai exports to China, the second biggest market in 2015 after the United States, slid 9.5 per cent from a year earlier in December and by 5.4 per cent for 2015.

Shipments to Europe rose 2.3 per cent in December but fell 5.7 per cent for the year. Those to the United States shrank 7.2 per cent last month but were up 0.7 per cent in 2015.

Imports dropped 9.23 per cent in December from a year earlier, and 11.02 per cent for 2015.

Mr Che-Yu Liang, a director of Ya Thai Chemical Co, which produces surface finishing chemicals for autos and other goods, said China's slowdown has impacted business.

"Many clients will bargain more to pay less, a 5 to 10 per cent discount, but they don't necessarily buy less from us due to the economy there," he said.

Last month, the central bank cut its 2016 economic growth projection to 3.5 per cent from 3.7 per cent, and predicted 2.8 per cent for 2015. Growth data for 2015 is due on Feb 15.