Southland Mayor Rob Scott said inspections of water and wastewater infrastructure last night did not turn up any damage
But he said some residents had been in touch about possible damage, including cracks to their homes.
At 9.14pm yesterday, a 5.9-magnitude earthquake, located 40km north of Te Anau and 53km deep, shook much of the region.
More than 18,500 people reported feeling shaking, according to the GeoNet website.
It was followed by a series of smaller aftershocks, which continued through the night and into this morning.
It was felt widely across the South Island, more strongly south of the Waitaki River, GeoNet said.
'Distinctly different'
GeoNet's Bill Fry said he was surprised by the geometry of the earthquake, saying the striking angle was unusual.
"It's really distinctly different to most of the earthquakes that happen."
He said it was a significant quake for New Zealand, but was not big enough to cause a tsunami, and lasted less than a minute.
"It's the type of shaking that starts to get to the threshold that it could cause some concerns."
GeoNet initially said the quake's magnitude was 6.3. Fry said a change in reported magnitude happens when they needed to make a rapid estimate to a large natural hazard.
He said they accept the uncertainties involved in this process, and prioritise getting the information to communities fast.
Fry said a 4.3-magnitude aftershock quake came within an hour of the initial quake, with a series of multiple about magnitude-4 aftershocks after.
He advised people that if they feel an earthquake longer than a minute, especially for those on the coast, they need to self-evacuate.
A further update is expected around 8.30am.
Bridge reopens
Queenstown Lakes District Council last night said the Edith Cavell Bridge at Arthurs Point would be closed overnight and inspected by engineers this morning.
In an update about 8.25am today the council advised that the bridge had reopened.
"Engineers have inspected the bridge this morning and are happy for it to reopen. Roading crews are onsite now removing traffic management to allow traffic to flow.
"Thanks to everyone for their patience!"
The council last night also advised people travelling over the Crown Range to drive carefully and be alert for rocks or debris that may have fallen on to the road.
Southland Mayor Rob Scott said this morning there did not seem to be any further problems.
He says the Southland District Council will be looking into why its website crashed during the emergency.
Meanwhile the only road into Milford Sound was closed for much of the morning, as a precaution following last night's earthquake.
NZTA said SH94 from Te Anau to Milford Sound will re-open subject to inspections of bridges, tunnels, retaining walls and any rockfall.
It re-opened about 10.30am today.
There are no restrictions on traffic out of Milford.
A Te Anau resident said the shaking was long and loud.
‘‘It sounded like a train.
‘‘A few things fell off the walls and the windows rattled so hard, it sounded like they’d break.
‘‘The walls were definitely moving.’’
Te Anau had earthquakes relatively often, but strong ones were unusual, she said.
She was not aware of any wider damage yet.
Social media in Dunedin also lit up with descriptions of the shake.
‘‘Heard the rumble and thought that’s a big truck ... then it was rocking and rolling,’’ a Dunedin resident said.
A Mosgiel resident said it was ‘‘damn huge’’.
There were reports of the shake being felt strongly in Queenstown and Wānaka.
The National Emergency Management Agency (Nema) and ESNZ Science last night issued a tsunami warning for the West Coast from Milford Sound south to Puysegur Point.
Nema said all people in the area should immediately move to the nearest high ground, out of tsunami evacuation zones, or as far inland as possible.
Some Southland residents have expressed concern on social media about communication from civil defence and local authorities following last night's earthquake.
An Emergency Management Southland post late last night acknowledged "mixed information around the magnitude and what people should be doing", and noted the Civil Defence website was down.
'You cannot always rely on technology', NEMA says
The National Emergency Management Agency (NEMA) said the Civil Defence website, which crashed following last night's earthquake, is just one part of any emergency response.
An evacuation order was issued, then downgraded, when the 5.9 quake struck just after 9pm, 40km north of Te Anau at a depth of 53km.
NEMA's John Price said on Friday an emergency mobile alert was issued to around 30 to 40 people living near Milford Sound within 10 minutes of the earthquake.
"[It] was very clear to us that a tsunami threat needed to be issued for Milford Sound requiring evacuations," Price told RNZ.
"That is what was done. NEMA issued the emergency mobile alert to the impacted area less than 10 minutes after receiving the advice from Earth Science New Zealand. It's all about keeping people safe at the end of the day."
Put to him that the quake was perhaps a dress rehearsal for a potential "big one" along the Alpine Fault, Price said a "rigorous debriefing process to identify what went well and what we can do better next time" will be undertaken.
"You cannot always rely on technology. It is one of the things that we do use. Of course, the [emergency mobile alert] is one tool, radio is another tool, and we ask people to use their own human danger sense."
Price said the "number one thing" was to "rely on our own ability as humans to actually do the right thing. Technology is just an enabler."
He said we live in "the second most dangerous country in the world".
"The Alpine Fault… there's a 75% chance that will go off in the next 50 years at a magnitude-8 plus. We do live in a very vulnerable area. People need to be prepared, they need to have a plan and they need to be able to activate their own danger sense, supported by the likes of NEMA.
"And we are there not only just to respond and recover, but to help people prepare as well."
He said it was impossible to be "100%ready".
"We need to move along that spectrum of readiness, and we need to be very mindful of it."
- Additional reporting RNZ
