The company told the Shanghai Stock Exchange that the 64,000-dwt options have been declared for delivery in 2017.
Last year, the owner made an initial order of two ships, adding another four in December.
The ships are said to be costing $26.5m each.
China Merchants Energy Shipping (CMES) has maintained its newbuilding push with four more ultramax bulkers at Chengxi Shipyard.
The company told the Shanghai Stock Exchange that the 64,000-dwt options have been declared for delivery in 2017.
Last year, the owner made an initial order of two ships, adding another four in December.
The ships are said to be costing $26.5m each.