Its Jiangsu New East Marine Engineering will build six firm 64,000-dwt vessels, with five sets of options for another six each.
The total series of 36 would be worth $974m, or $27m per ship.
JES said the client was a company registered in the British Virgin Islands which is backed by two private investment funds.
TradeWinds first broke the news earlier this month, revealing newly formed Chinese company Ample Oceans was behind the deal.
Sources say it is made up of a consortium of both private and public company investors from across multiple industries, including shipping, commodities, property, infrastructure and project-management.
The first six ships will be delivered between December 2015 to January 2016.
Options can be exercised next year for delivery from late 2016 on.
The deal brings JES’s new business this year to $436.4m, with options worth $1.1bn.
TradeWinds has also reported that Stamatis Molaris-controlled Empire Bulkers of Greece penned up to 18 capesizes worth $1bn at JES in April.
The order consists of 10 firm vessels plus eight options.
The 180,000-dwt bulkers are said to be priced at between $55m and $56m each. JES is scheduled to deliver the first in October next year, with the rest due to be handed over in 2016.
Regarding the Chinese order, JES said the SDARI1 design is “a model well sought after in the market now, is environmental friendly and fuel efficient.”
CEO Jin Xin added: “We are pleased to announce that we have just secured our largest contract fleet to date, marking our fourth contract win in under five months.
“Going forward, we will continue to seek for more opportunities in order to maintain our order winning momentum.”
