Cliffs have collapsed in New Zealand during an earthquake in the city of Christchurch on the South Island.

No serious damage or fatalities were reported in the Valentine's Day quake that struck at 13:13 local time (00.13 GMT).

Beaches to the east of Christchurch were busy with swimmers and surfers when rocks began to fall into the sea.

The 5.7 magnitude quake occurred days before the anniversary of a deadly one in 2011.

That destroyed the city centre and killed 185 people.

New Zealand lies on the notorious Ring of Fire, the line of frequent quakes and volcanic eruptions that circles virtually the entire Pacific rim.

'Ground started to go soft'

New Zealand's seismological body GNS Science classified Sunday's earthquake as "severe", recording that it took place at a depth of 15km (nine miles) and 15km to the east of the city.

Resident Stephen O'Dwyer said he was on the beach with his wife walking their dog when the cliff in Sumner started to collapse.

"The ground started to go soft. Water was coming up under the sand and people were sinking down to the ankles as the ground went soft. It shook for about 20 seconds," he told the BBC.

The quake sent large clouds of dust billowing over the suburb.

"I have to say that it was business as usual 15 minutes after the fact," said local Richard Loffhagen, who took a photograph of the dust and debris rising from Scarborough Beach.

During the tremor, which was reportedly felt across the South Island, some shops in Christchurch were evacuated and photos on social media showed items that had fallen off shelves.

A Polish couple posted a clip on YouTube showing the cracks their house suffered, saying it was their first experience of an earthquake in Christchurch and they had not expected it to be so intense.