A series of earthquakes have terrified many already-frazzled Christchurch residents this afternoon, starting with a 5.8 magnitude tremor at 1.58pm.

Initial reports said one person had received minor injuries, although St John had responded to 19 earthquake-related emergency calls in and around Christchurch.

They ranged from complaints of chest pain and seizures, to a panic attack.

Five people had collapsed, and one suffered a knock to the head.

St John said all injuries were minor.

Police say there is no tsunami threat, and they have no reports of serious or widespread damage or injury.

People were urged to stay away from hill suburbs because of risk of rockfalls, and Coastguard had rescued four people who were trapped by rockfall in Boulder Bay.

Police said there had also been a significant rockfall at Redcliffs, a stopbank on New Brighton Road had collapsed, a partly demolished building on the corner of Barbadoes and Kilmore Streets collapsed, and a vacant house at 81 Aynsley Terrace collapsed.

Major holes in the road were reported to have opened up on Broadhaven Avenue, and liquefaction was reported in Avonside.

Drivers were urged to slow down and be patient as congestion built up in some areas.

Police said Christchurch residents should stay off roads if at all possible, and text rather than phone.

Christchurch Hospital, the Princess Margaret Hospital and Hillmorton are all fully operational. Burwood is operating on emergency power.

There are no reports of damage and no injuries to staff or patients who were at the board’s facilities at the time of the quake.

The DHB said people can access 24-hour non-emergency care through their general practice, and are asked to help keep the Emergency Department clear for genuine emergencies. The 111 service is operating normally for emergencies.

The Christchurch mayor said his heart breaks for Cantabrians shocked by a series of earthquakes this afternoon.

The first, a magnitude 5.8 tremor, struck at 1.50pm. Its focal point was at a depth of eight kilometres, 20km off the coast of Lyttelton.

Mayor Bob Parker has now booked to fly back to Christchurch from Taupo, where he was holidaying.

He told TVNZ he was getting a lot of reports in from the east of the city of minor damage.

“On the east there’s more reports coming in of liquefaction, in Avondale … and there’s small collapses around riverbanks.”

He said while initial reports tell of minor damage to the city, today’s shake would have taken a large emotional toll on people.

“Many of them just sitting around and in tears. You just can’t understand the ongoing stress.”

“We were just getting over that feeling, I think, and it sets people back.”

He said the city had been told to expect an earthquake in the range of a magnitude six, which he thought had arrived.

He said council staff would already have dispersed across the city to check for damage to bridges, buildings and roadways.

Chlorine had finally been removed from the waterways two weeks ago, and today’s quake could have set infrastructure progress back, he said.

He was confident Cantabrians were strong enough to recover from today.

“We’ll get over the original shock. It’s just going to be one hell of a day. My heart just breaks really.”

The second major jolt of the afternoon’s swarm struck at about 3.18pm, and had a “rumbling, violent, rolling action” according to TV3 anchorman Mike McRoberts.

Mark Waller, managing director of EBOS Group said it “… was a really big one, I’d say if would be bigger than the 5.8 [at 1.58pm]. It felt like the February big one … it lasted for about a minute and a half.

Mr Waller said the tremors knocked his computer off his desk and “emptied cupboards in the office”.

Electricity distributor Orion reports power is out from the New Brighton area through to Shirley. It is thought 15,000 customers in the eastern suburbs including New Brighton and Dallington were without power. Electricity was also out in Springston in central Canterbury.

Orion said its crews were out assessing damage. It said it appeared power is out due to tripping caused by shaking rather than damage to equipment.

The Christchurch City Council has established an Emergency Operations Centre in the city. There has been a rockfall behind containers at Scarborough, and liquefaction at Parklands, the council said.

Police are doing aerial reconnaissance to check for damage across the city.

All Council buildings will be closed until they can be assessed as safe to occupy. People should assume all Council buildings are closed until they can be assessed and declared safe.

Cantabrians are being warned that more aftershocks could be on the way before Christmas.

GNS seismologist Ken Gledhill told TVNZ “this is part of a series of earthquakes that have been set off by what happened in September 2010.

“In the coming days the most likely scenario is that there will be a series of aftershocks in a similar location.

“This is just a reminder that this area is more active than what it was before September 2010.”

He said GNS were doing the best they could with information and the situation in Christchurch.

– APNZ