The incident at the Estlink 2 interconnector cable will not affect Finland's power supply, said Finnish Prime Minister Petteri Orpo.
Finland said it was investigating an outage involving a power cable linking it with Estonia under the Baltic Sea.
The unplanned outage occurred on the Estlink 2 interconnector on Wednesday at 10:26 GMT (11:26 CET), according to operator Fingrid.
"Even at Christmas the authorities are on standby to investigate the matter," Finland Prime Minister Petteri Orpo said in a post on X, adding the outage would not affect the Finnish population's power supply.
Authorities in the region have been on high alert for potential acts of sabotage following a string of outages of power cables, gas pipelines and telecom links in the Baltic Sea in recent years, although underwater cables are also subject to technical malfunctions and outages caused by accidents.