BEIJING (Reuters) - Shares at major listed steelmakers in top producer China slid on Tuesday as fresh tariffs by U.S. President Donald Trump stoked concerns over possible impact on steel exports this year.

Trump substantially raised tariffs on steel and aluminum imports on Monday to a flat 25% "without exceptions or exemptions" in a move to aid struggling domestic industries, but which increases the risk of a multi-front trade war.

Shares at Baoshan Iron and Steel, HBIS Co, Angang Steel, Hunan Valin Steel Co, Shandong Iron and Steel Co, Jiangsu Shagang Co slipped between 0.3% and 2.84%.

Steel prices on the Shanghai Futures Exchange also slipped by more than 1% in the morning trading session.

Fears mounted that new tariffs will add more uncertainty to China's steel exports this year, already threatened by mounting trade tensions, although the impact on direct Chinese steel exports to the U.S. is limited given the small share of the trade flows.

Last year, China's direct steel exports to the U.S. stood at 890,000 metric tons, just 0.8% of its total exports that hit a nine-year high at 110.72 million tons, customs data showed.

China's robust steel exports had helped to offset dwindling domestic demand, dragged by the protracted property crisis and the lower-than-expected consumption from the infrastructure sector last year.

"If the tariffs were to be implemented stringently, both direct exports and transit trade will feel some impact," analysts at consultancy Fubao said in a note.

Transit trade, or transshipment, refers to the process of countries buying products - in this case, cheap steel from China - and reselling those cargoes to other countries such as the U.S. to avoid tariffs or other restrictions.

A manager at an East China-based steelmaker, requesting anonymity as he is not authorised to speak to media, cautioned of "a butterfly effect on the market, which takes time to manifest."

"The bad news has not started yet, so we need to be prepared from now," the manager said, declining to disclose further details.

(Reporting by Amy Lv and Lewis Jackson; Editing by Lincoln Feast.)