Nine people admitted to Daisy Hill Hospital in Newry following a gas leak on a ship in Warrenpoint Harbour were expected to be discharged this evening.
A number of other people including ambulance personnel who were checked in the hospital for possible contamination were not admitted.
Work at the port has returned to normal and the cargo of grain will be unloaded shortly.
Two separate investigations have begun into the incident - one by the port authority and the other by the North's Health and Safety Executive.
Earlier, toxic gas used to kill rodents escaped from a ship docked at a harbour in Co Down.
Cargo on the vessel, the MV Arklow Meadow, at Warrenpoint, had become wet and unstable.
The gas was aluminium phosphide, a pesticide used to kill small mammals such as moles and rodents.
Operations at the port have resumed after the bags of pesticide were removed from the hold of the ship.
The vessel is owned by Arklow Shipping, based in Co Wicklow, and was built in South Korea in 2010.
Gardaí had been informed of the potential of the chemical compound to drift into Co Louth.
It was understood they were going house-to-house in the Omeath area advising householders to stay indoors and close all windows.
Louth County Council's Crisis Management Committee met to discuss the gas leak and its potential impact on homes on the Cooley Peninsula.
It said it was satisfied there was no imminent danger to residents and the leak appeared to have been contained within the Warrenpoint cordon.
The Council stood down their emergency measures after it was confirmed that the leak of toxic gas has been confined to the Warrenpoint area.
A spokesman for the NI ambulance service said nine people were taken to Daisy Hill Hospital and nine others were brought to Craigavon Area Hospital.
It said 15 of its vehicles were deployed and the incident was being treated as a major emergency.
Three hazardous area response teams were also deployed.
A number of homes in Warrenpoint were evacuated and a 50m cordon had been set up around the ship.