Construction on the world's biggest ultra deepwater semi-submersible drilling rig with dual drilling towers began last week in Yantai, East China's Shandong province.

Yantai CIMC Raffles Offshore Ltd Co, China's leading offshore engineering manufacturer and a subsidiary of the China International Marine Containers Group, is building the drilling rig, called Frigstad D90, for Norway's Frigstad Deepwater Co.

The Frigstad D90 has an overall length of 117 meters, a width of 92.7 meters and a height of 118 meters. It is designed to have a maximum vertical drilling depth of 15,250 meters, according to the builder.