GeoNet has issued a warning following a magnitude 5.5 quake this morning near Milford Sound.
The moderate quake hit at 3.24am, at a depth of 5km, and was 40km north-east of Milford Sound.
It was reported by more than 600 people around Queenstown and Wanaka.
People have posted on ODT's Facebook page to say also felt it in Cromwell, Clyde, Lawrence, Oamaru and Dunedin.
Anna Lewis was sleeping in Bannockburn at the time and thought she was dreaming, "But no the roof really did sway!"
Pam Henderson said she heard it coming in Glenorchy, while Ryan Barnes posted it was an alarm to get up and watch the cricket.
Although some at first weren't convinced it was a quake:
Vivienne Hunt, who lives in Jacks Point in Queenstown, told the NZ Herald said she was woken up by the tremors at between 3.30 and 4am.
"It felt like a large truck passing causing the ground to tremble and lasted a few minutes," she said.
Wanaka resident Julie Gillan said she woke up to her Venetian blinds and sliding wardrobe door rattling. Freda Lange, also from Wanaka, described the earthquake as very strong and lasted "at least five seconds".
The quake was part of a swarm of tremors around Milford Sound. The seismologist on duty at Geonet said it appeared to have occurred on the Alpine Fault.
"This fault system has the potential for larger events," Geonet tweeted.
"We would like to make sure that you are prepared for a large earthquake at all times."
The Alpine Fault runs hundreds of kilometres up the spine of the South Island, from Fiordland along the western edge of the Southern Alps.
- NZ Herald and ODT Online