Businesses around Petrie Plaza in Civic as well as Civic Library lost connection on Saturday afternoon.

Alan Nelson from Nelson and Co. Solicitors said it was "really not good" for their business.

"People can't contact us, can't send us documents, we can't send anything out. Our staff rely on internet for work. We even had to send one girl home because we didn't have work for her," Mr Nelson said.

Juliana Ratz from ITP Canberra City said she had spoken to many businesses around Petrie Plaza, including inside the Canberra Centre, who had been having the same problem as them.

"We haven't had any internet all day and have barely even had any phone connection. It is affected us really badly. Today is a cut off for a lot of people for new clients to process some of the last returns, so October 31 is a significant deadline date for taxes and it's really going to affect us," Ms Ratz said.

An iiNet spokesman said a circuit breaker tripped in a business in the area that was "outside iiNet's control" on Saturday.

One hundred businesses were affected by that trip from Saturday to Sunday however a secondary problem with iiNet's VDSL card meant a further nine customers were without phone and internet.

The spokesman said the problem was resolved by 10am on Monday and by 2pm, the businesses reported their services had come back online.

Canberra Centre manager Amanda Paradiso confirmed the original problem was a "a Transact issue caused by a circuit breaker failing over the weekend".

"Transact internet system services a large portion of the Canberra CBD and therefore this affected many other properties including Canberra Centre."

TransACT is a subsidiary of iiNet. iiNet was taken over by TPG last year.

While the iiNet spokesman maintained it was not their tech that originally caused the outage, he apologised to affected customers and the company will "do what we can" for them.