Two explosions and a fire were reported at a site run by Russia's second-largest natural gas producer on Sunday.
The blasts, where a gas tank is thought to have exploded, were reported at Novatek's chemical storage facility at Ust-Luga port, 100 miles southwest of St Petersburg, according to local media.
A statement given by the company to media outlet RBC said they were the result of "external influence" and that operations at the site had been paused.
A separate local news outlet reported two drones flying towards St Petersburg on Sunday morning. Kyiv has not commented.
Yuri Zapalatsky, head of Kingisepp, the district where the port is based, said there were no casualties, but the area has been placed on high alert.
Sky News could not independently verify the reports.
According to the Russian defence ministry, there has been no drone activity reported in the district, but four Ukrainian drones were shot down over the Smolensk, Oryol and Tula regions.
There was also a Ukrainian drone shot down on the outskirts of St Petersburg on Thursday.
Over the border in Ukraine, 25 people died on Sunday after shelling at a market in the city of Donetsk.
Twenty people, including two children, were also injured in the strike in Tekstilschik, according to occupying Russian authorities in the region.