U.S. corn surged more than 1 percent to a record high on Thursday as investors swept into the market ahead of a key U.S. government report that is expected to slash its production estimate another 15 percent due to damage from the worst drought in 56 years.

Soybeans leaped 3 percent as the drought kept eating away at that crop as well and wheat rose more than 1 percent in step with corn and soy and on crop worries in Russia's lush Black Sea wheat growing belt.

Recent rains and moderating temperatures in the Midwest farm belt, where the drought is centered, are not expected to help the corn crop in the world's largest grains exporter, with prices rising nearly 60 percent, or about $3, since May.

Soaring corn prices have authorities around the globe worried about rising food prices, just four years after the food crisis of 2008 sparked riots in many countries and added to unrest in Egypt that eventually led to the Arab Spring uprisings.

Dry weather has also cast a shadow over grains production in eastern Europe, while the monsoon season in India, crucial to the populous country's agricultural sector, has been weak.

Analysts said anecdotal accounts from the harvest of the first few fields in scattered areas of the U.S. Midwest show yields coming in low. The region accounts for 75 percent of all the corn and soybeans grown in the United States.

"People are putting risk premium back in ahead of the USDA report tomorrow. Early corn yields are making shorts very nervous. There are a lot of sub 100 bushel yields reported and that makes people fear the worst," said Dan Cekander, analyst for Newedge USA.

A Reuters poll of 21 analysts this week pegged the U.S. corn yield at 127 bushels per acre, the lowest since 1997, with production at a six-year low.

The U.S. Department of Agriculture (USDA) August crop report, to be released at 7:30 a.m. CDT (1230 GMT) on Friday, has taken on extra importance since the department's estimates will be based on surveys of farmers and its own experts inspecting fields for the first time since the drought began to rally prices in mid-June.

New-crop December corn futures rose to $8.29-3/4 per bushel, the highest price ever for a Chicago Board of Trade corn futures contract and above the previous record of $8.28-3/4 that was set by the spot September contract three weeks ago.

There were several bullish inputs to the markets.

Traders were moving or rolling long holdings in front-month September corn into the December and other new-crop contracts, preparing for a bullish government crop report and in step with the periodic rolling of positions undertaken by a Goldman Sachs index fund.

"The Goldman roll started Tuesday, you have that going on and the report is tomorrow. Everyone is expecting the corn number to be pretty friendly," a CBOT trader said.

Also, "there's talk China bought 3 to 4 cargoes of beans and looking for more, so there's a lot going on," he said.

Soybeans soared 3 percent as the drought kept trimming U.S. crop prospects, as China surfaced this week buying U.S. soybeans and as traders banked on further demand from the world's largest buyer of the oilseed.

"Beans continue to be driven higher by more new-crop sales to China," Cekander said.

The U.S. government on Thursday said China bought 165,000 tonnes of U.S. soybeans, boosting China's total purchases for the week to 271,000 tonnes. Each cargo of soybeans holds 55,000 tonnes.

Wheat rose in step with the gains in corn and soybeans, and on worries about weather stress in Russia's lush Black Sea wheat growing region.

At 11:55 a.m. CDT (1655 GMT), CBOT September corn was up 10 cents per bushel at $8.20-3/4 and new-crop December was up 7 at $8.23-1/2.

Most-active November soybeans were up 38 cents at $16.19-1/4 per bushel and September wheat was up 12 cents at $9.11-1/4.

On the weather front, modest amounts of rainfall in portions of the Midwest this week will provide only minimal relief from drought, an agricultural meteorologist.

"There will be some improvement, the cooler temperatures certainly will help. But most of the Midwest has not had enough rain for significant improvement," said Andy Karst, meteorologist for World Weather Inc.

"Crops may stabilize or decline a little more the next couple of weeks," he added.

Rainfall this week totaled 0.25 to 1.00 inch and was scattered over about half of the Midwest, but only about 25 percent received the heavier amount.

"There will be better rains today in the eastern Corn Belt, and the good news is that high temperatures the next couple of weeks will be in the 70s to 80s degrees Fahrenheit rather than 100 F," Karst said.

But "certainly no drought busting rains," he stressed.