Rescue efforts are continuing in New Zealand's second city, Christchurch, to reach at least 100 people who are thought to be trapped under the debris of buildings destroyed in a powerful earthquake.
The quake - measuring 6.3 on the Richter Scale - struck shortly before midnight Irish time and left at least 65 people dead.
New Zealand's Prime Minister John Key has said that the toll may rise as others are still trapped in the wreckage of collapsed buildings.
It was the second quake to hit the city in five months and New Zealand's worst natural disaster for 80 years.
The Department of Foreign Affairs has said 200 Irish nationals are registered in Christchurch.
It says it has general concerns about 70 of those and serious concerns about five. A spokesman said their priority is to locate all of these people.
Anyone with concerns regarding family or friends can contact the department on 01-4180222, and register details online on its travel registration system.
Authorities in New Zealand have set up an international helpline - + 64 78502199.
'We may well be witnessing New Zealand's darkest day...The death toll I have at the moment is 65 and that may rise,' Prime Minister Key told local TV.
'It's hard to describe. What was a vibrant city a few hours ago has been brought to its knees,' added Mr Key, who had flown to Christchurch.
The earthquake struck when the streets and shops thronged with people and offices were still occupied.
Christchurch's mayor described the city of almost 400,000 people as a war zone.
The quake is the country's worst natural disaster since a 1931 quake in the North Island city of Napier that killed 256 people.
Christchurch Hospital saw an influx of injured residents.
'We've had a lot of people at the emergency department ... a significant number, a lot of major injuries,' said David Meates, the chief executive of the Canterbury Health Board.
'They are largely crushes and cuts types of injuries and chest pain as well,' he said, adding some of the more seriously injured could be taken to other cities, where hospitals have been put on alert and prepared to accept casualties.
All army medical staff have been mobilised, while several hundred troops were helping with the rescue, officials said.
Emergency shelters have also been set up in local schools and at a race course.
Helicopters dumped giant buckets of water to try to douse a fire in one tall office building. A crane helped rescue workers trapped in another office block.
Emergency crews picked through the rubble, including a multi-storey office building whose floors appeared to have flattened on top of each other.
Christchurch is built on silt, sand and gravel, with a water table beneath.
In an earthquake, the water rises, mixing with the sand and turning the ground into a swamp and swallowing up sections of road and entire cars.
TV footage showed sections of road that had collapsed into a milky, sand-coloured lake right beneath the surface. One witness described the footpaths as like 'walking on sand'.
Unlike last year's even stronger tremor, which struck early in the morning when streets were virtually empty, people were walking or driving along streets when the shallow tremor struck, sending awnings and the entire faces of buildings crashing down.
Police said debris had rained down on two buses, crushing them, but there was no word whether anyone had been killed or injured.
The quake hit at 12.51pm (23.51pm Irish time) at a depth of only 4km (2.5 miles), according to the US Geological Survey.
