A Te Ānau worker described seeing cars "rolling around in the carpark" when a magnitude 6 earthquake struck the lower South Island this morning.

The moderate quake was centred 40km west of Milford Sound, in Fiordland at a depth of 5km.

Te Ānau Helicopters employee Helen Archer said she and another worker at the site were still feeling "sea-sick" after what felt like a 20 to 30-second earthquake.

"We certainly felt it. We've got cars out the front here and they were just rolling around in the carpark there.

"It was just rolling. The two of us here feel a bit car-sick or sea-sick still."

Residents of Queenstown, Wanaka, and Dunedin also all reporting feeling strong shaking.

A 4.2 magnitude aftershock struck at 10.25am - 25km west of Milford Sound at a depth of 8km.

Nearly 3000 people have reported feeling it, mostly in the lower South Island.

Multiple residents in Queenstown felt it and said there was a rumbling for about 15 seconds, the ODT says.

One Dunedin homeowner told the Herald she felt a short rocking motion, lasting only a few seconds, while a Wanaka resident said her windows rattled.

A spokesman for Fire and Emergency NZ southern communications centre said they hadn't yet received any calls or reports of damage in the area.

Several residents of the the lower North Island also felt the quake.

Just before 10.30am, 22 people reported it feeling like a "strong" quake, while three dubbed it "severe."

Three others said it felt "extreme."

More to come