GeoNet has issued a warning following a magnitude 5.5 quake this morning near Milford Sound.
The 3.24am quake was 5km deep and reported by more than 600 people around Queenstown and Wanaka.
It was part of a swarm of tremors around Milford Sound this morning.
The seismologist on duty at Geonet said the quake 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."
Viltare Veckyte, who lives in the Queenstown suburb of Frankton, had been in bed last night when the quake hit. She couldn't pinpoint the time but "it was quite [a] strong feeling of our bed [shaking]. It lasted for a second".
Vivienne Hunt, who lives in Jacks Point in Queenstown, 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.
It was her first time experiencing an earthquake after having lived the last seven years in Singapore and in Auckland before that.
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".
Nicola Spicer, who had just returned from living in Bali and having lived through earthquakes that had killed hundreds, woke up shaking in her bed.
"I think it is very important that people know how severe these earthquakes can be and plan an exit plan wherever they stay," Spicer said.