Invercargill Mayor Tim Shadbolt has warned of "blood on the floor" as he seeks to sack his deputy, Neil Boniface.

The mayor shocked fellow councillors last night, telling a full city council meeting he had "completely lost confidence" in Mr Boniface, the Southland Times reported.

"... This is going to be a very divided and fighting council ... I will go into the next elections fighting and there will be a lot of casualties."

Mr Shadbolt said he was tired of councillors privately pledging support, then not backing him up when it came to a public vote.

The mayor had earlier in the meeting tried - and failed - to replace Mr Boniface with another councillor, Geoff Piercy.

Mr Shadbolt said he would call a special meeting for councillors to debate whether Mr Boniface should remain deputy mayor.

- NZPA