One man has died in a blast at a water treatment plant in County Londonderry.
Ambulances attended the scene of the blast
Two others were injured in what police say was an industrial accident at Carmoney treatment works in Eglinton. A tank was blown through the roof.
The cause of the explosion is not yet known. However, there is no threat to the water supply in the city of Derry.
Eoin Doyle of the Fire and Rescue Service said firefighters in protective clothing managed to carry out a snatch rescue of an injured man at the plant.
"This was a tricky operation for our crews because there were chemicals and there had been an explosion," he said.
A major incident was declared over fears fumes from chemicals may have escaped.
Residents in the Eglinton and Campsie area were advised to stay indoors before the area was declared safe.
Altnagelvin hospital in Londonderry put its major emergency plan into effect.
A spokesman for the ambulance service said two people had been taken to the hospital, but their injuries were not life threatening.
A police spokesman later said: "We are treating the cause of this explosion as accidental."
Geoff Ennis, who works at a motor dealership just a few hundred yards from the plant, heard the explosion.
"We heard the bang and I was walking out the workshop door out to get mileage off one of the vehicles.
"I looked up in the sky and saw this huge tank. It was about 150-200 ft above the factory on the hill.
"At first, I thought it was a hot air balloon or something that had blown up, it was up at such a great height. I had a closer look and it was like a storage tank, falling to the ground then."
It is believed there was a construction team on the site as well as several Water Service employees.
It is believed that the plant may be closed for some time and that the Water Service is making arrangements to ensure the continued supply of water to the Waterside area of Londonderry.
Northern Ireland Regional Development Minister Shaun Woodward offered his sympathy to the families of the dead and injured.
He has asked to be kept informed about the condition of the injured workers.
"Water Service is liaising closely with the Health and Safety Executive, who will conduct a full investigation into the incident," he said.
The area's MP, SDLP leader Mark Durkan, expressed his sympathies to the dead man's family and praised the work of the emergency services.
"It seems that they have handled the emergency professionally and with great speed and they should be commended," he said.