The most active corn futures on the Chicago Board of Trade were up 0.4% at $4.52 a bushel by 0621 GMT, after closing up 2% on Thursday.

Corn on Tuesday hit its highest since June 2014 at $4.64 a bushel. Analysts said fears that U.S. production will not meet official estimates due to the recent wet weather were driving gains in prices.

"Lower yield forecasts are a good reason for corn prices to rally," said Tobin Gorey, director of agricultural strategy, Commonwealth Bank of Australia. Despite climbing in recent days, corn prices are at similar levels to the end of last week, when they rose 9%.

The most active wheat futures were down 0.1% at $5.26-1/4 a bushel, after closing up 1.8% on Thursday.

Wheat is down more than 1.5% for the week, set for the first weekly loss in six weeks. The most active soybean futures were down 0.4% at $9.12 a bushel, after closing up 1.4% on Thursday. Despite edging down, soybeans are up nearly 2% for the week, on course for their second straight weekly gain.

Soybean traders are turning their attention to next week's G20 summit, where U.S. President Donald Trump and his Chinese counterpart Xi Jinping are expected to meet.

An ongoing trade war between Washington and Beijing has slowed U.S. soybean exports to China, the world's top importer of the oil seed.