BEIJING (Reuters) - China's economy is expected to have slowed in the first quarter in the face of a prolonged property downturn, as policymakers brace for the impact of hefty U.S. tariffs that analysts say pose the biggest risk to the Asian powerhouse in decades.

President Donald Trump has ratcheted up tariffs on Chinese goods to eye-watering levels, prompting Beijing to slap retaliatory duties on U.S. imports in an intensifying trade war between the world's two biggest economies that markets fear will lead to a global recession.

Data on Wednesday is forecast to show China's gross domestic product (GDP) grew 5.1% in the January-March quarter from a year earlier, slowing from 5.4% in the fourth quarter, according to a Reuters poll.

The outlook is expected to dim further as Washington's tariff shock hits the crucial export engine, heaping pressure on Chinese leaders as they try to keep the world's second-largest economy on an even keel and prevent mass job losses.

A string of recent data has pointed to an uneven economic recovery, with bank lending beating expectations and factory activity picking up speed. But higher unemployment and persistent deflationary pressures are fuelling concerns over weak demand.

Moreover, analysts say a surge in China's March exports - driven by factories rushing shipments to beat the latest Trump tariffs - will reverse sharply in the months ahead as the hefty U.S. levies take effect.

"Before the tariff storms hit, China's GDP growth likely eased but remained solid, thanks to the recovery in domestic demand," analysts at Societe Generale said in a note.

"Overall, the GDP report should show that stimulus is working, but the support will not stop here with bigger tariff challenges ahead. The policy put is on."

While several other countries have been swept up in U.S. tariffs, Trump has targeted China for the biggest levies.

Last week, Trump lifted duties on China to 145%, prompting Beijing to jack up levies on U.S. goods to 125% and dismissing U.S. trade actions as "a joke".

On a quarterly basis, the economy is forecast to have expanded 1.4% in the first quarter, slowing from 1.6% in October-December, the poll showed.

Separate data for March is expected to show retail sales, a key gauge of consumption, rose by 4.2% after gaining 4.0% in January-February, while factory output growth is expected to ease to 5.8% from 5.9% in the first two months.

The government is due to release first quarter GDP data, along with March activity data, at 0200 GMT on Wednesday.

For 2025, the economy is expected to grow at a subdued 4.5% pace year-on-year, the poll showed, slowing from last year's 5.0 pace and falling short of the official target of around 5.0%.

UBS has downgraded its forecast on China's 2025 growth to 3.4% from 4%, on the assumption that Sino-U.S. tariff hikes will remain in place and that Beijing will roll out additional stimulus.

"We think the tariff shock poses unprecedented challenges to China's exports and will set forth major adjustment in the domestic economy as well," analysts at UBS said in a note.

AMPLE ROOM FOR STIMULUS

Policymakers have repeatedly said the country has ample room and tools to bolster the economy and premier Li Qiang this month pledged to roll out more support measures.

Beijing has put boosting consumption as the top priority this year as they try to cushion the impact of the Trump administration's tariffs on its trade sector.

The Politburo, a top decision-making body of the ruling Communist Party, is expected to hold a meeting later this month to set its policy agenda for the coming months.

In March, China unveiled fiscal measures, including a rise in its annual budget deficit. Officials have flagged more fiscal and monetary stimulus to cope with rising headwinds. That followed a blitz of monetary easing steps late last year.

Earlier this month, Fitch downgraded China's sovereign credit rating, citing rapidly rising government debt and risks to public finances, suggesting a tricky balancing act for policymakers seeking to expand consumption to guard against a trade downturn.

(Reporting by Kevin Yao; Editing by Shri Navaratnam)