The Nord Stream 1 pipeline restarted following a 10-day maintenance break but at a reduced level.
On Wednesday, the European Commission urged countries to cut gas use by 15% over the next seven months in case Russia switched off Europe's supply.
Russia supplied Europe with 40% of its natural gas last year.
Germany was the continent's largest importer in 2020, but has reduced its dependence on Russian gas from 55% to 35%. Eventually, it wants to stop using gas from Russia altogether.