When Trustpower's head office opens, there would be an additional 400 people in the city centre every day spending their money.
A number of co-working spaces had also started up in the city centre.
Priority One's Ignition opened in 2012 and expanded last year due to demand. It now houses more than 40 people who used to work from home in the suburbs.
There were three other co-working spaces in the city centre including Basestation which opened this month.
Griffiths Merchants Trust, which owns the building on the corner of Wharf and Willow Sts, pulled it down due to earthquake-strengthening issues.
Property manager Diane Rice said: "The original building was very old and would have been costly to repair to reach a satisfactory earthquake standard."
At this stage it did not know how many tenants it would have as it had not started marketing and there was no firm completion date, she said.
Insight Architecture director Matt Hodson said the new building was about 380sq m and covered two floors. "The proposed building is an extension of the existing building that is adjacent and has been designed to be complementary," Mr Hodson said.