A 5.3 magnitude earthquake has rocked Christchurch early this morning, GNS Science reports.

The aftershock was centred 20km west of Christchurch, at a depth of 15km, striking the city at 3.04am.

GNS Science said the quake was "widely felt around Canterbury", with many Cantabrians reporting the jolt was "slightly damaging".

The aftershock is the second largest to strike following the devastating 6.3 magnitude earthquake on February 22.

It was also the 25th earthquake Canterbury has had measuring five or more on the Richter scale since the 7.1 magnitude earthquake on September 4.

Prime Minister John Key said the quake has not caused any further considerable damage, but it "gnaws away at the confidence of Cantabrians who want this to end and for things to return to normality".

Mr Key is due to visit the city on Thursday.

A Fire Service southern communications spokesperson said there were no callouts following the quake.

Police said the only calls they had were from staff wondering if they needed to come to work.

New Zealand Herald reporter Jarrod Booker said the quake was "fairly violent".

"It gave the house a good shake," he said. "It was noticeably larger than previous aftershocks."

On social networking site Twitter Cantabrians shared their experience of the jolt.

"That #eqnz is close to home - no wonder it felt so dam powerful! and broke the window," Deon Swiggs tweeted.

"The Sky TV broadcast of the Liverpool FC game doesn't start until 6.55am. Up too early! Should have set that shake for later," Bob Hall tweeted.

"I wonder if The Grand Chancellor Hotel is still standing?" David Jones wrote.

There is no visible change to the Hotel Grand Chancellor this morning. The 26-storey building is still on a lean awaiting demolition.

Power remained on throughout the tremor.

GNS Science seismologist Caroline Ashenden said it was definitely one of the bigger aftershocks, but was not unexpected.

"We forecasted between zero and two aftershocks greater than 5 in the month between the 19th of April and 19th of May and this is the second one we've had," she said.

Newstalk ZB's Jo Scott, said the constant shaking doesn't get any easier, especially when they come in the middle of the night.

"We've had a total now of 5490 aftershocks and it's not nice. It's definitely something that is hard to deal with. It's very hard for people in Christchurch, especially when they're woken."

Canterbury residents have told Newstalk ZB they feel exhausted and under siege.

"You feel like soldiers, you're hanging in there but people are only human and they do break down," one caller said.

The aftershock has been followed this morning by a 3.4 magnitude quake at 6.06am, centred 10km southwest of Christchurch at a depth of 5km.

The 5.3 shake measured 6 on the Mercalli scale which measures ground shaking. That means it would have been difficult to stand, items are likely to fall off shelves and there will be plaster damage to some houses.

- with Newstalk ZB