AN EXPLOSION at a nuclear power plant on France’s northwest coast on Thursday caused minor injuries, but the authorities said there was no risk of radiation.

The blast occurred in the engine room at the Flamanville plant, which lies 25 kilometres west of the port of Cherbourg and just across from the Channel Islands.

“It is a technical incident. It is not a nuclear accident,” senior local official Jacques Witkowski said.

He said a ventilator had exploded outside the nuclear zone at the plant, which has been in operation since the 1980s and is operated by state-controlled energy giant EDF.

“It’s all over. The emergency teams are leaving,” Mr Witkowski said.

Five people suffered smoke inhalation but there were no serious injuries, Mr Witkowski said.

One of the two pressurised water reactors at the plant was shut down after the explosion and the incident was declared over at 1100 GMT (10pm AEDT), the authorities said.

The two 1300 megawatt reactors have been in service since 1985 and 1986, and the site currently employs 810 people, along with an additional 350 subcontractors.

A new third-generation reactor known as EPR is being built at Flamanville, which will be the world’s largest when it goes into operation in late 2018.

“Explosions in turbines, usually related to oil in bearings overheating, are not uncommon and occur from time to time in conventional coal, oil or gas plants,” said Barry Marsden, a professor of nuclear graphite technology at the University of Manchester.

But Neil Hyatt, a professor of radioactive waste management at Sheffiled University said the incident should not be taken lightly.

“Any incident of this kind at a nuclear power plant is very serious, and the national and international regulators will want to undertake a thorough investigation to understand the cause and lessons to be learned,” he said.

Construction of the new reactor at Flamanville began in 2007 and was initially due for completion in 2012 but has been delayed several times, and its initial budget has more than tripled, to 10.5 billion euros ($11.2 billion).

EDF said its safety record at nuclear sites improved last year, with 2.3 accidents for every one million hours worked, compared with 2.6 accidents in 2015.

That translates into five accidents that required reactor shutdowns in 2016, after eight the previous year.

France relies heavily on nuclear power, building its first nuclear plant in 1977 at Fessenheim, a site on the border with Germany that is set to be decommissioned in 2018.

Nuclear reactors generate about 75 percent of France’s electricity supply, a level the government wants to bring down to 50 percent by 2025.

Fessenheim, located on a seismic fault line, has worried French, German and Swiss environmentalists for years and its fate has been the subject of dispute with Berlin.

France and Germany are close EU partners but have taken vastly different approaches to power generation.

Germany — where the public mood swung against nuclear power following the 1986 Chernobyl disaster — decided to phase out nuclear power after Japan’s Fukushima meltdown in 2011.