Halifax's new sewage treatment plant on the waterfront is shut down indefinitely as engineers search for the cause of a malfunction, and that means raw sewage is again flowing freely into the harbour.

The malfunction occurred following a series of power failures on the peninsula on Wednesday but the search for the cause "could take quite a while," said James Campbell, spokesman for the $332-million Halifax Harbour Solutions project.

"It will be shut down for an extended period of time. It will have to be determined what exactly failed," he told CBC News on Thursday.

David Hendsbee, deputy mayor of the Halifax Regional Municipality, isn't impressed.

"It's a new plant," Hendsbee said. "Theoretically, it shouldn't have happened."

Hendsbee said officials told him that the power failures triggered the plant's backup generators, but something went wrong when the power came back on.

"There was a surge or something and it blew out the system. The sewage kept coming in. The chambers filled up and flooded the facility," he said.

"Now they have to pump it out, clean it out and dry it out. Then check the equipment. We may have electrical issues. There may be circuits, components that need to be replaced."

The malfunction occurred less than a month after the municipality took ownership of the plant from the builders.

The HRM took the keys on Dec. 17 after accepting the project was "substantially complete."

For months, municipal officials had refused to take it over, claiming there were problems with the system, particularly in backups and odour.

Campbell said part of the ongoing investigation will be to determine if any of the earlier problems were responsible for this week's malfunction.

The plant is under a three-year warranty.

Hendsbee said Halifax regional council will meet next week behind closed doors to discuss the malfunction.

With files from Paul Withers