A man has been left with burns to his mouth after an assault outside Nelson City Council offices early this morning.
The man suffered solvent burns to his mouth and throat in the attack, which happened around 6.45am, police said.
The man was taken to Nelson Hospital, where he remained this afternoon, police said.
The attack was being treated "extremely seriously", Constable Nick Kempthorne said.
"This is a cowardly attack with potentially serious consequences and we are very keen to find out who is responsible," he said.
Anyone who was in the area of the Trafalgar St - Halifax St intersection around the time of the attack, or who has any information that may help identify the offender, is asked to contact police.
Anyone who has CCTV footage of the stretch of Trafalgar St between Bridge St and Halifax St is also asked to contact Mr Kempthorne on 03 546 3840 or anonymously contact Crimestoppers on 0800 555 111.