* Corn up for 3rd day, jumps to highest since June 2013

* Soybeans hit their highest level in nearly seven years

* China issues guidelines on cutting corn, soymeal in feed

* Front-month soyoil hits 10-yr high on tightening supplies

SINGAPORE, April 21 (Reuters) - Chicago corn climbed to its highest in nearly eight years on Wednesday, rising for a third straight session, underpinned by worries over cold weather hurting the newly-planted U.S. crop.

Wheat rose for a second consecutive day, while soybeans advanced for a seventh session in a row to their highest in nearly seven years.

High feed grain prices are likely to take a toll on demand.

China's agriculture ministry published guidelines on Wednesday for the reduction of corn and soymeal in pig and poultry feed, in a move that could reshape trade flows of grains into the country.

"There is definitely a longer-term underlying bullish story, although the rally on the back of U.S. weather has come too early," Ole Houe, director of advisory services at brokerage IKON Commodities in Sydney, said.

"There is plenty of time to get corn and beans in the ground."

The most-active corn contract on the Chicago Board of Trade (CBOT) was up 1% at $6.12-3/4 a bushel by 0802 GMT, after hitting its highest since June 2013 at $6.14-1/2 a bushel earlier in the session.

Soybeans were up 0.7% at $14.68 a bushel, having climbed to a June 2014 high of $14.72-1/4 a bushel earlier on Wednesday. Wheat gained 0.5% at $6.64-1/4 a bushel.

Worries about cold weather slowing germination of the 2021 U.S. crop supported prices.

Meanwhile, a Reuters poll of 11 analysts showed Brazil's 2020/2021 total corn crop could reach a record 107.3 million tonnes, even as the country's second corn crop was planted outside the ideal climate window.

Corn may test a resistance at $6.42-1/2 in one or two weeks, a break above which could lead to a gain to $7.21-1/2, Wang Tao, a Reuters analyst for commodities technicals, said.

"The contract has cleared a lower resistance at $5.79. It is likely to extend gains into $6.42-1/2 to $7.21-1/2 range," he added.

Tensions in related vegetable oil and biodiesel markets added to the strength in soybeans. Traders have sold two shipments of Ukrainian rapeseed this month to Canadian buyers, a highly unusual trade, market sources said.

The CBOT front-month soybean oil contract rose to its highest since June 2011 at 59.20 cents per lb.

Global commodity prices are expected to stay firm around current levels in 2021 after recovering in the first quarter buoyed by strong economic growth, the World Bank said on Tuesday.

Commodity funds were net buyers of CBOT corn, soybean, soyoil, wheat and soymeal futures contracts on Tuesday, traders said.

(Reporting by Naveen Thukral; Editing by Subhranshu Sahu and Alexander Smith)