The seventh unit of the Tianwan Nuclear Power Plant in eastern China's Jiangsu Province is witnessing a crucial phase in construction.

Friday's work saw the bottom tier of the inner containment dome lifted into place.

The engineers lifted and hoisted the belt and the top separately due to limited space at the construction site. 

The dome's belt is 12 meters tall, weighs about 375 tonnes and was lifted by a 2,000-tonne crawler crane on Friday morning onto the unit and adjusted into the exact position. Thousands of workers and technicians at the site coordinated with each other through every step of the process.

The whole process took about three hours, and the accuracy of the lift and hoisting is controlled at the millimeter level, according to a personnel at Tianwan.

"Moving the crawler crane is like walking a tightrope. You can't even deviate a bit from the route. But thanks to our shared experiences and analysis, we succeeded. It's the result of combined efforts of thousands of us at the site," said Wen Xin, chief crawler crane operator for the mission.

Next month, the upper tier of dome will be completed, signifying the conclusion of its two-year construction work.

A total of five years is needed to complete the structure alone, which is deemed one of the most sophisticated structures in the world. The next phases will include installation work inside the building, as well as testing.

The Tianwan Nuclear Power Plant is one of the biggest nuclear energy bases in the world and will have eight power units once completed.

"Both use advanced third-generation nuclear power unit technology," said Wang Luyang, an engineer at Jiangsu Nuclear Power Corporation.

"They have a capacity of 1.26 million kilowatts, and when both are complete, our total installed capacity with eight units will be over nine million kilowatts. This will provide 70 billion kilowatts of clean energy per year," he said.

The engineers said that the new units represent the growing trend of more secure power with enhanced safety measures.