* S.Korea Dec exports +7.1 pct y/y, better than expected
* Shipments to U.S., China up sharply
* Policymakers see continued recovery in 2014
* Yen weakness seen as a key growth risk
(Updates with details on exports, background)
SEOUL, Jan 1 (Reuters) - South Korean exports grew by an annual 7.1 percent in December, beating forecasts and pointing to Asia's fourth-largest economy sustaining momentum into the new year, though there are increasing concerns about the impact of a weak Japanese yen.
Several of South Korea's big industries -- automobiles, ships and steel -- compete fiercely with Japanese rivals, and authorities are worried that the Korean won's rise to a five-year high against the yen will hurt their competitiveness.
Shipments from South Korea, the world's seventh-largest exporter, were $48.1 billion last month, while imports grew an annual 3.0 percent to $44.4 billion.
That led to a trade surplus of $3.7 billion, data from the Trade, Industry and Energy Ministry showed on Wednesday.
Export growth was slightly stronger than the median forecast of 6.4 percent in a Reuters poll, and well above the 0.2 percent recorded in November.
The data is another sign of economic momentum that should be maintained into 2014. The Bank of Korea expects quarterly economic growth of at least 0.8 percent in the fourth quarter, in seasonally adjusted terms, following growth of 1.1 percent in the two prior quarters.
For the full year, exports grew 2.2 percent while imports shrank by 0.8 percent, resulting in a trade surplus of $44.2 billion. The finance ministry expects exports to grow by 6.4 percent in 2014, benefiting from a gradual global recovery.
YEN WEAKNESS A RISK
State-owned Export-Import Bank of Korea has said it expects exports in the first quarter to grow by around 10 percent from a year earlier because of better external conditions.
That would be double the growth of 4.8 percent in the final quarter of 2013, which was best growth in two years, Reuters calculations show.
Indeed, exports to the U.S. rose by an annual 13.2 percent in December, while exports to China rose by 8.4 percent. Shipments to the European Union rose 2.0 percent.
However, Seoul is concerned about the impact on its exporters of the depreciation of the yen as Tokyo uses massive fiscal and monetary stimulus to try to escape deflation.
This week, bid rates for the yen fell to a five-low under 10 won, and it has weakened by nearly 30 percent against the South Korean currency over the past 15 months.
The deputy finance minister expressed concern about the yen's rapid decline, and the trade ministry on Wednesday warned that the weak yen poses a threat to exports.
Policymakers have said they will consider countermeasures, though they have declined to elaborate. Currency dealers suspect authorities could buy dollars to indirectly keep the won from rising further against the yen.
(Reporting by Se Young Lee; Editing by Choonsik Yoo and John Mair)