Britons caught up in the Christchurch earthquake have spoken of the chaos and devastation in New Zealand's second largest city.
At least 65 people have died after a 6.3-magnitude earthquake struck the city at lunchtime on Tuesday.
One British backpacker said it "looked like a bomb had hit it".
The Queen said she was "utterly shocked" by the quake. The Foreign Office said it was "urgently" seeking information about British casualties.
Christchurch was still trying to recover from a 7.1-magnitude quake in September, which left two people seriously injured but no fatalities. It caused an estimated $3bn (£1.9bn) in damage.
Although stronger, the previous quake happened in the middle of the night and its epicentre was further away and deeper underground.
'Running on jelly'
Barnaby Luck, from Haverfordwest in Pembrokeshire, was in a hostel when the disaster hit at 1251 local time (2351 GMT on Monday).
The 29-year-old, who has been travelling in New Zealand since November, said: "It was like someone had got hold of the building and was shaking it back and forwards, so I just jumped under my bunk bed.
"Once it stopped I was really shaken up and went outside. I only realised the magnitude of it when I looked up the street.
"The gable side of a building 100 yards away was completely levelled to the ground and as I made my way into the centre of the town, there was just total devastation."
Gavin Blowman, from Hull, said he was coming home. The 33-year-old graphic designer has been living in New Zealand for two years but said he was not sure he could continue living with the threat of earthquakes.
He said he ran from his office when the earthquake struck and it was like "running on jelly". His home in the coastal suburb of Sumner has been badly hit so he and his friends took sleeping bags and tents and drove up into the hills after hearing a rumour about a tsunami.
"We met a Christian couple who live up here who have let us stay in their caravan," he said. "There are still fires and smoke in the centre of town and the bay is drained of water."
Backpacker Christopher Ratcliffe, 27, from Sutton Coldfield, West Midlands, was forced to shelter under a desk in a library.
"When I came outside the city looked like a bomb had hit it," he said.
"There was dust and smoke in the air and bits of glass and rubble falling from the tops of buildings. People were walking around covered in blood and in tears - it was just shocking."
Alison Stokes, originally from Birmingham, was at home with her child and father when the earthquake struck.
"The house was picked up like something from The Wizard of Oz and shaken for what seemed like a minute. It was absolutely terrifying," she said.
"I couldn't get in contact with my husband for three hours. It was horrible because I was seeing on the news that there had been fatalities. Fortunately, everyone in my family is fine."
A state of emergency has been declared in the city with reports of people being trapped in buildings. The authorities are warning the death toll is likely to rise. The airport is closed and Christchurch Hospital, the largest in the South Island, has been evacuated.
In a message of support to New Zealand Prime Minister John Key, the Queen said: "Please convey my deep sympathy to the families and friends of those who have been killed; my thoughts are with all those who have been affected by this dreadful event.
"My thoughts are also with the emergency services and everyone who is assisting in the rescue efforts."
Defence Secretary Liam Fox said he would be speaking to his New Zealand counterpart and the UK would offer the country any help needed.
Foreign Secretary William Hague said: "Many people in the UK with links to New Zealand will be watching anxiously as the situation develops.
"Our High Commissioner in New Zealand is on her way to Christchurch and we stand ready to provide any assistance that we can to the authorities and to any British nationals who have been caught up in the earthquake."
Britons in New Zealand can telephone the High Commission on 04 924 2898 for assistance, or the Global Response Centre in the UK on 0044 207 008 1500.
The New Zealand High Commission in London is advising New Zealanders in the UK who are worried about friends and family to monitor the government's official websites, media reports and try to make direct contact.
It also advised those due to travel to Christchurch to contact their airline or travel agent. All other South Island and New Zealand airports are open.
Christchurch is home to about 350,000 people, and is considered a tourist centre and gateway to the South Island.
New Zealand sits on the Pacific Ring of Fire, a vast area of seismic activity, and records more than 14,000 earthquakes a year, although only about 150 are felt by residents.