NEW YORK (Reuters) -Shares of U.S. refiners fell to near two-year lows on Friday in the wake of U.S. President Trump's announcement of new tariffs, as fears of slower fuel demand and weakening refining margins rattled investors.

Top refiners Marathon Petroleum ( MPC ), Valero Energy ( VLO ) and Phillips 66 have shed more than $20 billion in market capitalization since Trump announced sweeping new tariffs on Wednesday, based on LSEG data.

Nations around the world have readied retaliatory tariffs and on Friday, China, the world's top oil importer, announced it will impose additional tariffs of 34% on all U.S. goods from April 10.

"We consider the adoption of the 'reconciliatory tariffs' will result in weaker global GDP growth and so lower oil demand growth, oil prices and weaker refining margins, as exemplified by the futures markets over recent days," Alan Gelder, vice president of refining, chemicals and oil markets at Wood Mackenzie.

Crude futures closed at their lowest in more than three years on Friday, with Brent diving 6.5% to $65.58 a barrel and U.S. West Texas Intermediate crude slumping 7.4% to $61.99.

For the week, both benchmarks tumbled nearly 11% in their biggest weekly loss in percentage terms since 2023.

The impact on crude was more instantaneous than on U.S. gasoline and diesel futures, which in comparison fell about 8% in the week.

However, the new levies are fueling a trade war that will weigh on the global economy and the consumption of refined products, analysts said.

"While crude oil and refined products have been range-bound for most of the year battling the constant tariffs and sanctions hot air, this implementation of sweeping tariffs has forced the market to re-examine demand," energy analysts at Rabo Bank said in a note.

The refining sector is already over-supplied and so its margin recovery is heavily dependent upon the trajectory for demand growth, Wood Mackenzie's Gelder said.

Global gasoline demand is expected to peak this year at around 28 million barrels per day (bpd) amid surging electric vehicle adoption and improving vehicle efficiency, particularly in China, according to S&P Global Commodity Insights. Diesel demand is likely already declining after reaching 29 million bpd last year.

"We are now expecting much lower demand growth in 2025 and in 2026, so not only do the tariffs stall the recovery in refining margins we previously forecast in 2026, but they also drive refining margins lower, perhaps back to 2021 levels," Gelder said.

Shares of Marathon, which is the top U.S. refiner by volume, fell nearly 6% at $121.07, their lowest since July 2023, on Friday.

Valero, the No. 2 U.S. refiner by capacity, dropped around 8% to $104.69, the lowest since May 2023.

Phillips 66's shares decreased around 8% to $98.81, the lowest since July 2023.

Meanwhile, the energy index sank around 6% on Friday.

(Reporting by Nicole Jao in New York; editing by Philippa Fletcher and Marguerita Choy)