Experts say the people of Canterbury should brace for more quakes like this morning's 5.1 tremor - probably every four to six weeks.
The quake, which struck at 6.03am was of the biggest tremors since September's big shake, but caused only minimal damage. It hit 10km southwest of Christchurch at a depth of 10km.
Christchurch Mayor Bob Parker said the aftershocks were frustrating and another "rude wake up call for the city" they would rather not have.
"There's a sense of 'is this ever going to stop' and I don't think anybody back on the 4th of September would have imagined that here we would be in 2011, in the middle of January, experiencing significant aftershocks.
"We seem to take a step forward and the next thing you know, we're back up here checking the buildings again.
"It doesn't matter the size of the aftershock, psychologically what it always does is bring back that intense feeling of fear and uncertainty."
GeoNet duty seismologist John Ristau said the aftershock was felt widely all over the Canterbury region as well as on the West Coast and in Oamaru.
Two more aftershocks, one measuring 3.4 and the other 4.0, were recorded in the area just after 8am and in the past 24 hours, there have been 21 tremors in the Canterbury region.
They ranged in magnitude from 2.7, up to the 5.1 quake this morning.
And Ristau said the aftershocks could even extend beyond the anniversary of the September 4 earthquake.
Social media outlet for fear
A flurry of tweets were posted on Twitter after today's quake some describing it as "massive".
One woman said it had set car alarms off on her street.
Residents also shared their experiences of the latest aftershock on the ONE News Facebook page.
"Things fallen over again!" posted Kim Eagle.
Rara Bunting said her house "felt like a giant had come along and given it a wee shake".
And Steph Thorpe summed up what many Cantabrians are probably feeling today:
"When will it end?"
The latest earthquakes will be treated as a 'new event' by the Earthquake Commission.
"This adds to the list of what we are treating as separate events. These are the 7.1 earthquake on 4 September, the 5.0 aftershock on 19 October, the 4.9 on 14 November, and the 4.9 on Boxing Day," the chief executive of EQC, Ian Simpson, said today.
But the damage hasn't been as bad as on the Boxing Day quake.
"The Boxing Day earthquake ... was actually much closer to the Christchurch City Centre and it was actually quite a bit shallower too," explained Ristau.
People who felt it worst were those who live near Halswell, near its epicentre.
Carmel Turner from the Halswell Bakery described the quake as "crazy".
"I was just coming in to turn all the lights on, and the whole place started to shake, made a real horrible noise like it was going to fall down around my ears," she told ONE News.
Simpson said claims appear so far to be for relatively minor damage such as some cracking of interior and exterior walls and the exacerbation of existing damage.
By mid-afternoon, the EQC had received 53 claims for damage from the latest aftershocks.