According to the GeoNet website, the quake struck at 9.14am (7.14am AEST) today, about 45km north of Geraldine at a depth of 10km.
Fire and Emergency New Zealand said there were no reports of damage. Civil Defence confirmed that New Zealand does not face a tsunami risk.
There are more than 14,338 reports on GeoNet of people feeling the shake, with majority based across the South Island.
Of those reports, 11 rated the quake as "extreme" and 169 as "strong". Since then, there have been nine unnoticeable earthquakes in the South Island, with magnitudes ranging between two and four.
Timaru resident Ferguson Sail was studying earthquakes in a civil engineering course when the shake struck.
"I just grabbed on to the table ... the chairs with wheels on moved around the room.
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"There are sirens going off all over the place.''
Meanwhile, a Geraldine resident saw fans in her café shaking, and felt "quite wavy". The quake lasted for at least a minute, she said.
There was no damage to the cafe that she was aware of, and one customer was inside when the quake struck.
The shake has also forced the closure of the three-storey Sophia St car park, next to the Farmers building in central Timaru.
GeoNet described the quake as "strong".
The quake's epicentre is near Christchurch – the city devastated by an earthquake in 2011.
The magnitude 6.3 quake struck in February 2011, leaving 185 people dead.
