Belgian power utility Electrabel said on Saturday that a nuclear reactor at its controversial Tihange plant near Liege automatically shut down after a fire broke out in a non-nuclear area of the facility.

Electrabel said in a statement that the automatic shutdown of the ageing Tihange 1 reactor on Friday night followed a "fire at the plant's power supply panel," noting it was in "the non-nuclear part" of the plant in eastern Belgium.

Electrabel said the shutdown of the reactor was the "normal procedure" for such an event and that a team was looking into what caused the fire, adding that the reactor could restart Tuesday.

The Tihange 1 is the oldest of the plant's three reactors. It has been running since 1975 and was due to be shut down in 2015, but the government decided in 2012 to keep it open until 2025.

The Belgian power utility restarted the Tihange 2 reactor last week after a near two-year shutdown.

Electrabel said it put the Tihange 2 reactor back on line "in complete safety," despite opposition from officials in neighbouring North Rhine-Westphalia, Germany's most populous state.

Belgium has been hit by a series of nuclear mishaps in recent years, with three of the country's seven reactors at one point closed, due in two of the cases to the discovery of micro-cracks in the reactor casings.