British nationals caught up in a deadly earthquake that is believed to have caused 'multiple fatalities' on New Zealand's South Island today spoke of the chaos and devastation following the crippling natural disaster.

The powerful 6.3-magnitude quake struck 10km outside Christchurch during lunchtime rush hour, about 1am British time, causing widespread destruction and injury.

Eyewitnesses said the 5km deep tremor, believed to be an aftershock from a 7.1 magnitude earthquake which struck last September, levelled high-rise buildings, tore up pavements and sprayed rubble on to the streets below.

A state of emergency has been declared in the city with collapsed debris and buildings trapping an unknown number of people.

British backpacker Christopher Ratcliffe, 27, was forced to shelter under a desk in Christchurch library when the quake struck.

'The building started to shake, my computer screen started to flicker and then the books started to fly off the shelves so I just dived under my desk,' said the traveller from Sutton Coldfield, West Midlands.

'I have experienced a few aftershocks before this, but this was totally different.'

'When I came outside the city looked like a bomb had hit it. 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.'

• Do you know anybody affected by the earthquake? Contact reporter Dan Grimmer on 01603 772375 or email daniel.grimmer@archant.co.uk