An explosion at the Dutch port of Rotterdam on Thursday killed at least one person and injured several others, city police said.

Police said the blast at Europe’s biggest port happened late Thursday morning and that a crime scene has been set up to try to establish what caused it.

Rotterdam emergency services reported a major power failure at the port and said that a transformer had caught fire under unexplained circumstances. Power was gradually being restored to companies in an industrial area of the port a few hours later.

A number of oil and gas companies are based there and fire crews were standing by.