Several injured people were taken to hospital, according to police, while forensic investigators and the Dutch labour inspectorate were sent to the scene. A damaged wall and signs of an explosion on a storage tank could be seen in the area as emergency services secured the site. Police spokesperson Daan Valkenburg said investigators were considering all possible causes and had not yet reached a conclusion.

The facility is operated by Gunvor Energy, which runs a refinery and fuel terminal in the sprawling port. Dutch broadcaster NOS reported that a maintenance team had been working on a section of pipes when the explosion occurred, but authorities did not confirm that account.

A separate power failure also affected another part of the port on Thursday, with a transformer catching fire, prompting several companies to halt operations and evacuate workers. Emergency services later said the blackout was not linked to the explosion. Police said the investigation would establish what happened.