* USDA estimates corn acres above expectations, soy below
* Wheat follows corn lower (Rewrites throughout with U.S. market open, adds quote, updates prices, changes byline, changes dateline from PARIS/SYDNEY)
CHICAGO, June 28 (Reuters) - U.S. corn futures plunged by the most in nearly three years on Friday after the U.S. Department of Agriculture (USDA) pegged U.S. planted acres well above trade expectations despite rains and flooding this spring that disrupted sowing.
Soybeans firmed on the USDA's smaller-than-expected acreage estimate, while wheat fell in tandem with plummeting corn prices.
In its annual acreage report on Friday, the USDA said U.S. farmers seeded 91.7 million acres of corn and 80.0 million acres of soybeans. This compares to the government's March forecasts of 92.8 million corn acres and 84.6 million soybean acres.
Analysts, on average, were expecting corn acres at 86.6 million and soybean acres at 84.4 million.
Corn futures dropped despite widespread belief the actual acreage figure was considerably lower.
"These are intentions of the farmers in the first two weeks of June so this is probably not what was actually planted. These numbers are certainly going to be subject to change, for corn and soybeans both," said Brian Hoops, president of Midwest Marketing Solutions.
Chicago Board of Trade September corn was down the daily 25-cent limit at $4.20-3/4 per bushel at 11:51 a.m. CDT (1751 GMT). The 5.6% drop was the steepest by a most actively traded corn contract since July 6, 2016.
New-crop December futures were also down the limit at $4.26 per bushel.
CBOT August soybeans rose 3-1/2 cents to $8.97-1/4 a bushel while new-crop November gained 2-3/4 cents to $9.15 a bushel.
CBOT September wheat fell 23 cents to $5.23-3/4 per bushel.
Soybeans drew some additional support from a surprise U.S. soybean sale to China announced by the USDA ahead of a G20 summit meeting on Saturday between U.S. President Donald Trump and China's Xi Jinping.
The USDA also released quarterly stocks data for corn, soy and wheat on Friday, although the market's focus was squarely on the surprising acreage estimates.
(Additional reporting by Gus Trompiz in Paris and Colin Packham in Sydney; Editing by Chris Reese)