French energy group EDF has formally asked the government for a three-year delay until 2020 to the deadline for launching its next-generation EPR nuclear reactor, according to a copy of the request seen by AFP Tuesday.

EDF had been set a 2017 deadline for switching on the European Pressurised Reactor (EPR), a third-generation reactor design considered the most advanced and safest in the world, when it began building it in Flamanville, northwest France, in 2007. But the project has been beset by technical delays leading to cost overruns.

The French group said last month the nuclear project was likely to go online towards the end of 2018.

In an October 9 letter to the France's energy ministry, EDF asked for the official deadline to be extended to April 11, 2020, so as to allow it "room for manoeuvre" in case of new developments without having to request further changes to a state decree authorizing its construction.

The French group is seeking to build two nuclear reactors with the same new technology in a 25 billion pounds (34-billion-euro) project at Hinkley Point in southern England.

According to French business daily Les Echos, China has agreed to take a 33.5-percent stake in the Hinkley Point project in a deal likely to be announced during Chinese President Xi Jinping's four-day state visit to Britain, which began Tuesday.

The completion of Hinkley Point, too, is likely to be delayed by two years until 2025, according to a report in the Financial Times.

The project in Flamanville had been set to be the first EPR reactor to go on line, but now it appears that could be achieved at the Taishan nuclear reactor in southern China.