A faulty signal was behind the automatic shutdown of the unit with no danger posed, Nebesar added. "It was a technical hitch," he explained, adding that the unit should be up and running normally Friday morning.

Temelin is regularly the target of Austrian protests against the Czech nuclear plant sited around 60 kilometres (38 miles) from the Austrian border. It has been beset by frequent faults and problems but Czech authorities say it operates in line with European regulations.

Austrian nuclear protesters blocked the border crossing at Wullowitz-Dolni Dvoriste for around six hours on Sunday.

They threaten to organise more blockades of the border if the Austrian governement does not raise an official protest against Czech authorities' decision to give final building approval for the long operational Temelin plant, at the start of November.

Protestors say the official move broke the Melk accord on power plant safety signed by the two countries in 2001 to try to mend relations poisoned by the Soviet-era designed unit which was built in 1987.