A 33 year-old man is being questioned following a serious assault in the Butetown area of Cardiff.
A 39 year-old man is in a crticial condition after he was assaulted on Hansen Street at just after 9am on Friday morning.
He was airlifted to the University Hospital of Wales in the city.
A police cordon remains in place at the scene of the incident with motorists advised to find alternative routes.
Anyone who witnessed the assault should contact South Wales Police on 101 or use the live web chat, quoting reference no. 2500032515.
Alternatively, phone Crimestoppers anonymously on 0800 555 111.