A jump in factory output and robust growth in services buoyed the Singapore economy to a larger-than-expected expansion in the third quarter of this year.

The economy grew 5.1 per cent in the July to September period over the same time a year ago, according to preliminary estimates released by the Ministry of Trade and Industry on Monday morning.

This beat economists' estimates of a 3.8 per cent expansion and was also higher than the year-on-year growth in the second quarter, which the Ministry revised up to 4.2 per cent on Monday.

But in quarter-on-quarter terms, the economy shrank 1 per cent in the third quarter from the second quarter, the Ministry said.

The year-on-year growth was boosted by a 4.5 per cent increase in the manufacturing sector. This was up from the second quarter's expansion of 1.3 per cent and was mainly due to transport engineering and electronics manufacturing.

Services industries expanded by 5.7 per cent in the third quarter, close to the healthy 5.6 per cent growth in the second quarter, supported by finance and insurance and wholesale and retail trade.

Construction, however, grew at a smaller pace in the third quarter: 3.6 per cent, down from 6.9 per cent in the second quarter. This was mainly due to weaker public sector construction activities, which partially offset robust construction activities in the private sector, the Ministry said.