Nuclear power utility TVO said on Thursday that there was an automatic emergency shutdown of its Olkiluoto 2 (OL2) reactor in southwest Finland.
The company said that a disruption occurred at 12.22 in which "an isolation of main steam lines has launched an isolation which has isolated also the containment" [sic].
The shutdown, known as a 'scram' proceeded as expected, TVO said.
Initially the company said it was preparing for a cold shutdown state, but it later retracted this statement.
TVO said there was no release from the plant and that "no harm has been caused on people or the environment" [sic].
The Radiation and Nuclear Safety Authority (Stuk) said that it was informed of the incident around 1pm.
The watchdog said at around 2.30pm that elevated levels of radiation were detected within the facility but that "according to information received by Stuk, the facility has not released radiation into the environment", adding that the radiation level in the surroundings of the plant were normal.'
The Olkiluoto plant, which has two reactors and a long-delayed third one still under construction, lies between Rauma and Pori on Finland's west coast.
Around 5pm, Stuk said that the situation was stable and that the plant was in a safe condition. It said that no radiation release has occurred or was expected and that local residents did not need to take any precautions.
The agency said that no employees had been injured or exposed to radiation.
"We do not see an acute threat," Stuk Director General Petteri Tiippana said in a statement.
5:22 Updated with latest Stuk statement.