The tanker, identified as Koala, was preparing to depart when an explosion occurred in the engine room. Reports from the security services-linked channel Baza indicate that three blasts were heard, prompting the 24 crew members to evacuate safely onto the pier.
The engine room was flooded, causing the vessel to settle by the stern and touch the seabed. Despite this, most of the ship remains afloat, and no pollution has been reported. All crew members are unharmed.
Official statements provide varying accounts of the incident. Russia's Marine and River Transport Agency stated that the tanker is not at risk of sinking and that the cargo tanks remain intact.
The governor of Leningrad described the event as a "man-made incident" during engine startup, adding that the tanker remains securely moored. Investigations into the cause are underway.
The Koala is a 22-year-old, Turkish-owned, Cypriot-managed Suezmax tanker with a capacity of 160,000 dwt.
The vessel, which has changed its flag state four times in the past year, has no recent record of deficiencies in port state control inspections.
In a separate maritime incident over the weekend, the Chinese bulk carrier An Yang 2 ran aground near Sakhalin in the Russian Far East on Saturday. Following these events, Finnish Prime Minister Petteri Orpo announced that Finland is monitoring the situation and has placed its oil spill response capabilities on alert as a precaution.