Eighteen people have received treatment after a toxic gas leak on a ship docked at a Northern Ireland harbour.

Potentially lethal fumes from a pesticide used to kill rats escaped when cargo on the vessel at Warrenpoint, Co Down, became wet and unstable.

Nine people including crew from the MV Arklow Meadow, which was carrying grain from Odessa in the Ukraine, and harbour workers were taken to hospital by ambulance after coming in direct contact with the gas. Nine others were treated at the scene as a precaution.

A spokeswoman for Daisy Hill Hospital in Newry said the men had been assessed and would be discharged.

In a statement, the Warrenpoint Harbour Authority said: "A cargo vessel containing grain was being discharged as normal. Staff noticed that several small packages of pesticide contained within the cargo had started to vaporise. We understand that the cargo of grain itself is not contaminated.

"The crew and staff were immediately evacuated from the ship and the port's emergency plan was enacted. Thirteen crew members and five Warrenpoint Harbour staff came into direct contact with the pesticide fume."

The gas is aluminium phosphide, a pesticide used to kill small mammals such as moles and rodents. Breathing it in can damage the lungs and cause wheezing or shortness of breath.

A 50 metre cordon was set up around the harbour. Dozens of homes and businesses were evacuated and the area was sealed off for over five hours. At the height of the drama, 15 ambulances including three hazardous area response teams and eight fire crews were sent to the scene.

A spokeswoman for the Northern Ireland Fire and Rescue Service said three crews would remain on standby at the harbour on Wednesday night as a precautionary measure. The vessel belongs to the Co Wicklow-based Arklow Shipping, which declined to comment on the leak.

South Down MLAs Caitriona Ruane and John McCallister have called for a full investigation into the cause of the incident.