St John Ambulance said two people were injured after the tornado hit the city.
Emergency services were called to the SaveMart second hand shop on Battersea St, Sydenham.
A St John spokesman said at least two people were injured after the tornado damaged the store's roof.
A SaveMart employee said the tornado ripped off parts of the roof. The store has now closed for the day while "the big mess is cleaned up", she said.
The woman confirmed those injured by the roof ripping off were not employees.
"It just threw everything around, it was carrying things over top of buildings. At first we were just watching a piece of cardboard getting blown around in a whirlwind. Then it started picking everything up," he said.
Wordsworth St, between Waltham Rd and Gasson St, has been closed to clear the debris.
Orion spokeswoman Linda McGregor said there are 1128 people without power across Canterbury as a result of the storm's impact on the network.
She said crews were on their way to affected areas at about 2.31pm to assess when power will be turned back on.
The tornado tore past Waltham School causing some of the branches outside the front of the school office to fall down.
Deputy principal Janine Tarawhiti said she first became aware of the tornado when a parent rushed to the school to check if the children were okay.
She said it was fortunate the tornado did not happen during the school’s lunchbreak and the school’s first priority to check all children were safe.
“I think they have taken it in their stride and have been quite excited…one child made a comment: “it must be Christmas because it is snowing outside”.
A post on the Beckenham Neighbourhood (Christchurch NZ) Facebook group said: "I've just witnessed a big tornado rip through Waltham area, evacuate if you need to.
"It came over ours. Swear I have bruises."
The tornado was accompanied by a heavy hailstorm, thunder and lightning.
The MetService issued a severe thunderstorm warning. It said the blast is now moving east across Christchurch.
The strike had blown fuses and blown power points off the wall.
No one was injured in the strike, he said.
One appliance from Palmerston attended.
Another appliance from Waikouaiti was turned around.
Metservice have issued a raft of weather warnings for the South Island today, with heavy rain, thunderstorms and even snow expected.
A severe thunderstorm warning is in place for Christchurch City, with lower warnings in place for North Otago south to Waikouaiti.
