A number of earthquakes felt in the Whanganui region during January have slowed progress on the redevelopment of the Sarjeant Gallery.
Redevelopment project director Gaye Batty said there was concern the movements would affect the 100-year-old building, which is undergoing seismic strengthening.
"There were quite a few shakes during January and we have had testing done to ascertain whether there had been any damage," Batty said.
"The reports showed that there had been no detectable movement caused by earthquakes or by the construction work."
In a report to the Whanganui District Council property and community services committee this week, Batty said work was now going "full steam ahead" on the strengthening of the old building.
"There is a batter - a sloping concrete wall in place where the trees used to be and A-frames beside the building to protect it during strengthening," she said.
"There is now visible progress on the new wing and the walls of the basement where the collection will be stored are coming out of the ground."
Batty said the new wing, which had a target completion date of August this year, is now likely to be completed in April 2022, which will coincide with the target date for the completion of work on the old building.
She said the delays have been caused by the unexpected length of time it took to build the batter and make sure it met compliance standards.
Archaeological finds at the new building site have also caused delays.
Councillors questioned Batty about the costs involved in financing the time extension and were assured that the costs would be covered by the contingency fund.
Batty said progress reports and photos of the redevelopment can be viewed on the Sarjeant Gallery website.