BEIJING, June 20 (Reuters) - China's soybean imports from the U.S. accelerated in May with a 156% surge from a year earlier, data showed on Thursday, while supplies from Brazil shrank for the first time this year amid flooding disruption in the South American country.

The world's biggest soybean buyer imported 1.27 million metric tons of the oilseed from the U.S. last month, compared with 494,103 tons in the same month a year earlier, showed data from the General Administration of Customs.

That was still far less than imports from Brazil at 8.8 million tons, which made up the majority of the 10.22 million tons of soybeans China imported in May.

Sales of U.S. soybeans to China has been sluggish this year as traders take advantage of cheaper and plentiful Brazilian soybeans.

Still, May arrivals from Brazil dropped 19% from a year earlier.

Brazil's soy harvest season that started around March is almost finished, that country's national crop agency said last week. The agency slightly lowered Brazil's soy production forecast after unprecedented rain in the southern part of the country damaged some of the crop.

For January-May, shipments from Brazil totalled 24.71 million tons, up 23% compared with the same period last year.

Total arrivals from the U.S. in the first five months of the year came to 10.85 million tons, down 34% on the prior year, the data showed.

China imported 212,492 tons of soybeans from Argentina in the five-month period, though the data showed no arrivals in May. (Reporting by Mei Mei Chu; Editing by Jamie Freed and Christopher Cushing)