A police investigation is underway following a serious assault at Auckland City Hospital in the small hours of Friday.

Police said two people were treated for their injuries after the assault, involving gang members, at 3.40am Friday.

Police were providing assistance to hospital security as a precaution, and to reassure staff.

Anybody with information can provide it to police on 09 302 6557, or anonymously to Crimestoppers on 0800 555 111.