* China Q4 GDP grows 4.0% y/y vs 3.6% forecast in Reuters poll
* China 2021 GDP grows 8.1% versus 8.0% forecast
* Dec factory output growth picks up, retail sales disappoint
BEIJING, Jan 17 (Reuters) - China's economy grew 4.0% in the fourth quarter from a year earlier, faster than expected but its weakest expansion in one-and-half years, National Bureau of Statistics data showed on Monday.
Gross domestic product (GDP) had been forecast to expand 3.6% from a year earlier, according to a Reuters poll of analysts, slowing from 4.9% in the third quarter.
GDP grew 8.1% in 2021, the data showed, faster than 8.0% expected by analysts.
On a quarter-on-quarter basis, GDP rose 1.6% in October-December, compared with expectations for a 1.1% rise and a revised 0.7% gain in the previous quarter.
China's economy got off to a strong start in 2021 as activity rebounded from a pandemic-induced slump the previous year, but it has lost steam due to a property downturn, debt curbs and strict COVID-19 curbs which have hit consumption.
Chinese leaders have pledged more support for the economy, which is facing multiple headwinds into 2022.
China's industrial output grew 4.3% in December from a year earlier, picking up from a 3.8% increase in November, official data showed.
The figure beat expectations of a 3.6% increase in a Reuters poll of analysts.
However, retail sales in December missed expectations with only a 1.7% increase from a year earlier, the slowest pace since August 2020. Analysts in the poll had expected them to grow 3.7% after rising 3.9% in November.
Fixed asset investment rose 4.9% in 2021, compared with the 4.8% increase tipped by a Reuters poll and 5.2% in the first 11 months of the year. (Reporting by Kevin Yao and Gabriel Crossley; Editing by Jacqueline Wong)
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