Novatek, Russia's largest liquefied natural gas producer, said on Sunday it had suspended some operations there blaming "external influence."
The Ust-Luga complex is on the Gulf of Finland, about 110 miles west of St. Petersburg.
The Interfax-Ukraine news agency, citing unnamed sources, said the fire was the result of a special operation carried out by Ukraine's security services.
It said fuel refined there is supplied to Russian troops.
Reuters couldn't confirm the cause of the fire.
Russian news outlet Shot said local residents heard a drone operating nearby followed by several explosions.
Alexander Drozdenko, the Leningrad region's governor, said on the Telegram messaging app there were no casualties and all workers were safely evacuated.
Russia and Ukraine have targeted each other's energy infrastructure in strikes aiming to disrupt supply lines and logistics in the nearly two-year-old war.
