Danish authorities have asked ships to stay away from a five nautical mile radius of the island of Bornholm after a gas leak overnight Monday from Russia's defunct Nord Stream 2 pipeline, which drains into the Baltic Sea.

"A leak occurred today in the Nord Stream 2 gas pipeline in the Danish area," the Danish energy agency said.

The German government said it was in contact with the Danish authorities and working with local authorities to find out what caused the sudden drop in pressure in the pipeline.

On Monday evening, the operator of the Nord Stream 1 pipeline, which had been running at reduced capacity since mid-June before completely stopping supplies in August, also revealed a drop in pressure on both lines of the pipeline.

"The reasons are being investigated," Nord Stream AG said on its website, without revealing further information.

The pipeline has been one of the turning points in an escalating energy war between Europe and Moscow since Russia's invasion of Ukraine in February, which has buffeted major Western economies and sent gas prices soaring.

The chairman of the German grid regulator, Klaus Mueller, said that the pressure drop in both pipelines "underscores the German grid regulator's assessment that the situation is tense."

"We are currently in contact with the authorities involved in order to clarify the situation. We still have no clarity on the exact causes and facts," reads a statement from the German Ministry of Economic Affairs.

The Danish maritime authorities had issued a navigation warning and established a zone around the Nord Stream 2 pipeline "because it is dangerous for ship traffic," he added.

The Nord Stream 2 operator said that the pressure in the pipeline, which had contained some gas sealed inside despite never becoming operational, dropped from 105 to 7 bar overnight.

The pipeline, which was intended to double the volume of gas flowing from St. Petersburg under the Baltic Sea to Germany, had just been completed and filled with 300 million cubic meters of gas when Germany cancelled it days before the invasion.