Part of Belfast's harbour estate was sealed of for several hours yesterday following an incident at a chemical plant.
Eyewitnesses described seeing a large plume of smoke above the Albion Chemicals plant on Seal Road following what was described by police as a 'chemical reaction'.
There were no injuries reported following the incident which happened at around 11am, although a 100-metre exclusion zone was put in place and people working in nearby offices and factories were told to remain indoors with the windows closed.
The reaction occurred while a chemical container was being cleaned out.
"It's directly across from us so we saw the large plumes of smoke coming out," said Vanessa Myers, who works at a nearby office.
"We didn't hear an explosion or anything. There were just very large plumes of orange smoke which went on for a while. Then the Fire Brigade came out and doused it for a short time."
Paul Neeson, who works as a depot manager at a site next door to the chemical plant, said he was not aware of any explosion either.
"I came out and had a look and just saw this big cloud of yellow smoke," he said.
"Once we saw the fire crews arriving we thought it was maybe better to leave the area.
"There wasn't really any panic, but once I saw the guys from the chemical plant walking outside I knew there was something wrong."
A spokeswoman for the Northern Ireland Fire and Rescue Service said: " Firefighters wearing chemical protection suits worked in liaison with the Albion Chemical on-site team to reduce the vapour being produced by the chemical reaction.
"Four fire appliances and a hazardous material unit were deployed to the scene.
"Firefighters deployed protective water sprays over the container to reduce fuming off."
A spokesman for the Environment and Heritage Service said drainage systems at the site were blocked to prevent any liquid material entering the port waters.