Authorities have stated there is no danger after a "serious" incident was reported at a nuclear power station in Finland.

The incident occurred in reactor 2 of the Olkiluoto power station, in the southwest of the country at 12.22 local time (11:22 CET).

But the Finnish nuclear safety authority (STUK) later confirmed that the situation was stable and the reactor had been shut down.

"A severe abnormal disturbance occurred at the Olkiluoto nuclear power plant unit 2," STUK said in a statement.

"The disturbance was possibly caused by a fault in the purification system for the reactor water... there was no radioactive release to the environment.

STUK added there was no need for protective measures and they did not expect any danger outside the unit. No workers or personnel had been exposed to radiation or injured in the incident.

"STUK started the emergency activities immediately in full force due to exceptionally high radiation levels inside the unit," said director general Petteri Tiippana.

"There are about 80 persons following the situation, but we do not see an acute threat."

About a third of Finland's electricity comes from nuclear power, with four reactors in operation and two under construction.