Updates at 0139 GMT

By Ella Cao and Lewis Jackson

BEIJING, April 3 (Reuters) - The Chicago Board of Trade (CBOT) saw declines in grain and soybean futures on Thursday as concerns grew that the new U.S. tariffs could trigger retaliatory actions against U.S. farm products, with over 40% of U.S. soybean production sold abroad.

The most-active soybean contract Sv1 on the CBOT fell 1.17% to $10.18 a bushel as of 0133 GMT, marking the biggest daily drop in a month.

Wheat Wv1 extended losses for a second consecutive session, dropping 1.48% to $5.31 a bushel, while corn Cv1 lost 1.15% to $4.53 a bushel.

On Wednesday, U.S. President Donald Trump announced a 10% baseline tariff on most imports to the U.S., with higher duties on dozens of countries, kicking into high gear a global trade war.

However, top trading partners of the U.S., Mexico and Canada, avoided fresh tariffs, although previous duties remain.

"Most of the tariffs have turned out to be more of a fizzle than a bang. What was initially proposed as a blanket 20% tariff has been reduced to just 10%, which is manageable for most nations," said Ole Houe of IKON Commodities in Sydney.

With Asia being a major market for U.S. grain, retaliatory tariffs - particularly from China - could make it more difficult for the U.S. to sell its products there, Houe added.

China, the world's biggest soybean importer, has already imposed tariffs on some $21 billion worth of U.S. agricultural products, including soybeans, fuelling expectations that China will look to boost Brazilian supplies.

As the world's largest soybean exporter, Brazil competes with the U.S. for sales to key markets like China. With a bumper harvest, Brazil is expected to boost China's second-quarter soybean imports to a record high.

The U.S. Department of Agriculture's (USDA) weekly data on U.S. wheat export sales on Thursday is expected to show a net cancellation of 100,000 metric tons, with net sales of 300,000 metric tons for 2024-25, analysts polled by Reuters said.

Weekly U.S. soybean export sales are forecast to range between 250,000 and 800,000 metric tons for 2024-25.

As farmers in the Midwest prepare to plant corn and soybeans, crop weather is being closely monitored. Heavy showers and thunderstorms have caused wind damage, large hail, and flash flooding in the Corn Belt, according to a USDA report.

(Reporting by Ella Cao and Lewis Jackson; Editing by Sumana Nandy and Janane Venkatraman)

((Ella.Cao@thomsonreuters.com;))