GNS says the quake measured 4.3 magnitude just after 3.30am. It was of strong intensity and was close to the central city - just 5km south of Christchurch. It was also just 5km deep and has been followed by several aftershocks.
Police said there were no reports of damage and no increased calls to emergency services.
The traffic signal fault, originally thought to have been caused by the quake, began around 10 last night, Christchurch Transport Operations Centre says.
The fault has now been fixed and congestion is expected to ease.
The transport operations centre says the signals team is working with the Christchurch City Council's IT department to find the cause.
Lousy start to week for many
Some of the city's rattled residents reacted on social media to the shake.
Roana Noah wrote on Facebook: "Happy leap day everybody, apparently that meant leap out of ya bed to save yourself from an earthquake..."
Euan Mason said: "Wheeee. That one woke me. Mag 4.3, but only 5 km deep and quite close (in Cashmere)..."
Meanwhile, Claire from New Brighton, east of the central city, thought the quake felt like it was bigger than a 4.3.
She told Newstalk ZB's Bruce Russell that she had to hang on to the kitchen bench.
Victoria Rutherford reported hearing booming noises like a canon, and Mike Yardley called the quake a heart thumper.
Yardley wrote on Facebook: "Thump...nasty shake in south Christchurch. 4.3 mag. Centred in cashmere. Only 5km deep! Yuck..."
Margaret Agnew also wished everyone a happy leap year - literally - and tweeted she hadn't done the down the hall dash to the kids in the night since ages ago.
Many more complained about it being a lousy start to the week.
Newstalk ZB reporter Scarlett Cvitanovich told early morning host Rachel Smalley that the quake hit right next to Cashmere High School.
She says a lot of people around the Sydenham, Cashmere, St Martins areas when they reported it felt like it was right under their houses, it actually was.
Ms Cvitanovich says it's been a while since people in Christchurch have been woken up by something so loud and violent.
She says it brings back memories of the September 2010 earthquake.
