Project director Geoff Cotton said work was about halfway through during a site visit on Wednesday.
About 100 workers were on site, but this was to increase in coming months.
The redevelopment is in the block bordered by Dee, Esk, Kelvin and Tay Sts, with the exception of the Kelvin Hotel and Reading Cinemas.
The project is a joint venture between Invercargill City Holdings Ltd (a subsidiary of the Invercargill City Council) and O’Donnell CBD Ltd.