Bucharest: Romanian authorities launched search and rescue operations off the Black Sea coast on Thursday after a fire broke out aboard a ship, leaving eight people missing. Four people were rescued.

The cause of the fire aboard the San Marino-flagged Wine Trader, a chemical tanker travelling from Tunisia to Romania, was not immediately clear. However, a recent spate of drone strikes on ships in the Black Sea has raised concerns about the Russia-Ukraine war spreading further.

There were 12 people aboard the ship when the fire broke out 13 nautical miles southeast of the port town of Sulina, according to the Romanian Naval Authority.

Romania's Ministry of National Defence said a “group of air targets” was monitored overnight near Ukraine's Snake Island. A drone briefly entered Romanian airspace at 1.34 am southeast of Sulina before disappearing from radar, the ministry added.

Similar drone incursions have occurred this month in the exclusive economic zones of Romania and Bulgaria, both NATO and European Union members.

The latest incident follows a fire aboard the Comoros-flagged chemical and oil tanker Yara J in Romanian territorial waters on Wednesday evening. The vessel, travelling from Turkey to Sulina, reported the fire to Romania's naval authority. Its crew was safe and had evacuated.

Romania's acting Defence Minister Radu Miruta said an investigation was underway, but no drone had been seen on military radars heading towards the Yara J.

The two ship fires come amid a series of incidents involving commercial vessels in the Black Sea. Five commercial ships have been hit off the coasts of NATO members Romania and Bulgaria since early October, with about 23 sailors dead or missing. The incidents have highlighted the growing threat that drone warfare linked to the Russia-Ukraine war poses to commercial shipping near NATO's eastern flank.

On Tuesday, drone strikes on two ships off Bulgaria prompted emergency rescue operations for 11 crew members from the HS Dignity, a Guinea-Bissau-flagged cargo ship. The crew members remain missing.

The other vessel, the Ukrainian-operated coastal freighter Chelsea 3, was sailing under a Maltese flag. Rescuers evacuated all 15 crew members, five of whom received treatment for minor injuries. The crew reported that the ship's deck and hull had been hit by three aerial drones. Bulgarian Prime Minister Rumen Radev said Russia was likely responsible for the Tuesday incidents.

A week earlier, sea and aerial drones struck two other commercial vessels in Bulgaria's exclusive economic zone in the Black Sea. A Togo-flagged ship sank, while a Bulgarian ferry evacuated the 18-member crew of a damaged Palau-flagged vessel.

On October 5, a Turkish-owned cargo ship carrying corn caught fire following a drone attack and later sank in the Black Sea off Romania's coast. Two people died, and 11 crew members were rescued.

(With inputs from AP via PTI and Reuters)