By Ziyi Tang and Joe Cash

BEIJING (Reuters) -China's factory activity expanded modestly for a second straight month in November, an official survey showed, adding to a string of recent data suggesting a blitz of stimulus is finally trickling through the world's second-largest economy just as Donald Trump ramps up his trade threats.

The National Bureau of Statistics purchasing managers' index (PMI) on Saturday rose to 50.3 - a seven-month high - from 50.1 in October, above the 50-mark separating growth from contraction and beating a median forecast of 50.2 in a Reuters poll.

The mood in China's manufacturing sector has been depressed for months due to tumbling producer prices and dwindling orders, but two months of positive PMI readings suggest the stimulus announcements are improving sentiment on factory floors.

That said, fresh headwinds from additional U.S. tariffs could threaten China's industrial sector next year and pour cold water over any early optimism in the Asian giant's manufacturing sector.

While there have been some signs that Chinese policymakers' latest moves may be lending support to the ailing property market, which has weighed heavily on domestic demand, officials are now in a race to limit the economy's vulnerabilities ahead of a second Trump presidency.

President-elect Trump said on Monday he would impose a 10% tariff on Chinese goods so that Beijing does more to stop the trafficking of Chinese-made chemicals used in the production of fentanyl.

He also threatened tariffs in excess of 60% on Chinese goods while he was on the campaign trail, hikes that pose a major growth risk for the world's top exporter of goods.

China's exports surged more than expected in October, which analysts attributed to factories rushing out shipments to major markets in anticipation of further tariffs from the U.S. and the European Union.

"The economy stabilized recently as fiscal and monetary policies eased after the Politburo meeting on September 26. But the outlook for 2025 remains unclear," said Zhang Zhiwei, president and chief economist at Pinpoint Asset Management.

"The trade war is looming and it will delay investment decisions by the corporates. The investors expect fiscal stimulus but the size and composition of spending are uncertain," said Zhang.

The central economic working conference in December may shed some light on the policy outlook, he added.

The PMI report showed total new orders expanded for the first time in seven months in November, while new export orders contracted for the seventh consecutive month.