China has begun to assemble a new cargo spacecraft that will be tasked with servicing the Tiangong space station, according to a key figure in the space station program.

Bai Mingsheng, a researcher at the China Academy of Space Technology and chief designer of the Tianzhou-series cargo spacecraft, told China Central Television on Sunday that the design work on the Tianzhou 6 has finished and engineers have begun to assemble the robotic craft.

"The Tianzhou 3, 4 and 5 were built in accordance with the previous technical specifications while the new craft, from Tianzhou 6 to 11, will be based on a set of upgraded specifications," he told the State broadcaster.

Bai said that compared with its predecessors, the Tianzhou 6 will have a redesigned cargo section and its airtight cabin will have greater carrying capacity.

The improvements will enable a new Tianzhou craft to operate for longer than before. Currently, the country needs to launch two Tianzhou ships each year to transport fuel and supplies to the Tiangong station. Upon the new model being put into service, three such craft will be enough to sustain two years of in-orbit operation for Tiangong, according to the designer.