Citic Group, China's oldest and biggest conglomerate, has agreed to sell a 20% stake to Japanese trading house Itochu and Thailand's Charoen Pokphand (CP) Group for around $10bn (€8.6bn, £6.6bn).
Citic, in a statement to the Hong Kong stock exchange, said it had signed an agreement with CT Bright, a venture equally owned by Itochu and CP Group, that will see the Japanese and Thai firms acquire a fifth of the Hong Kong-traded company.
The deal will take place in two stages, with Citic selling nearly 2.5 billion shares to Itochu and CP for HK$34.4bn in April this year, and a further 3.3 billion shares for HK$45.9bn in October.
CT Bright will own 20.6% of Citic post completion of the deal.
The investment gives Itochu and CP Group better access to the world's second-biggest economy.
Itochu is a diversified conglomerate that trades everything from gas to grain. CP Group is an agribusiness firm owned by Thailand's second-richest man Dhanin Chearavanont.
The stake sale helps Citic further broaden its investor base as part of Beijing's reforms of state-owned enterprises.
Some analysts said the deal, which will probably require borrowing from banks, appeared risky for Itochu.
Nomura Securities analyst Yasuhiro Narita said: "From a concentration risk perspective, it appears to be high risk.
"While Citic is a conglomerate, it deals with areas such as real estate and raw materials development which are facing deteriorating conditions, we need to note the possibility of future losses."
The deal marks the biggest investment made by a Japanese firm in China so far, according to Thomson Reuters data, beating a $1bn investment by automaker Nissan Motor in Dongfeng Motor in 2002.