One person has died and three others are being treated after losing consciousness aboard a cargo ship that had just docked at Denmark’s port of Hanstholm.

The four people, reported to be crewmembers of the ship, were found unconscious Tuesday evening in a confined area of the Polish-flagged MV Corina, which had just arrived in Hanstholm from Gdansk, Poland with a cargo of wood pellets. A fifth person is believed to have escaped the area.

Authorities suspect that the victims inhaled poisonous gasses, possibly carbon monoxide, from the wood pellet cargo.

The three injured are being treated at local hospitals.

It is unclear from reports if the crewmembers were in the cargo hold itself or in a confined space of the ship adjacent to the cargo hold.

Wood pellet cargoes are known to produce carbon monoxide and carbon dioxide, which can lead to a reduction in oxygen levels and the development of a dangerous concentration of carbon monoxide in closed spaces.

Wood pellets are listed in the International Maritime Solid Bulk Cargoes Code (IMSBC Code) as a hazardous “Group B” cargo.

The incident follows a similar accident earlier this month at the Port of Atwerp, where three longshoremen died after entering the cargo hold of a ship that was previously carrying a cargo of coal.