Eighteen people are being treated after toxic gas used to kill rodents escaped from a ship docked at a harbour in Northern Ireland.

Cargo on the vessel at Warrenpoint, Co Down, had become wet and unstable and a cordon has been set up.

The gas is aluminium phosphide, a pesticide used to kill small mammals such as moles and rodents. Police in the Irish Republic have been informed of the potential of the chemical compound to drift into their area.

A Police Service of Northern Ireland (PSNI) spokesman said: "It is believed that there are five casualties suffering from the effects of exposure to the gas."

But a Northern Ireland Ambulance Service spokesman said: "We have 18 patients. It is a chemical incident on a ship. Nine are en route to Daisy Hill Hospital and nine are at the scene and they will be transferred to Craigavon Area Hospital."

A Northern Ireland Fire and Rescue Service spokeswoman confirmed they were dealing with a major incident.

Sinn Fein Warrenpoint councillor Michael Ruane said a specialist large ambulance service truck was parked near the incident.

Emergency services have gathered in the main square and the town hall has been made available if people have to be evacuated.

Mr Ruane said: "The incident is confined to the harbour at this moment in time. The fire service and police seem to be keeping well back from it. There are a number of boats in the harbour - there are a number of small mussel boats and some larger vessels."

The ambulance service said 15 of its vehicles have been deployed: five accident and emergency ambulances, three hazardous area response teams, one paramedic rapid response vehicle, five ambulance officers, a doctor and an emergency equipment vehicle.