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.

Penarth Library shortlisted for Library of the Year Award
Keep Wales Tidy launch "Drive your litter home" campaign
Members return to the Senedd Siambr following redevelopment
Barry resident shares his story of Operation Pied Piper in new book
Council to engage with public over future of former Wilko Superstore in Barry
Former Conservative turn Reform candidate wins Penarth By-election
Two teenagers sentenced for murder of Kamran Aman in Barry
Council celebrates success of Solar Scheme with Relaunch
Vale Food Trail set to return for 2026
Centenary Year Begins as Barry Swimming Club Celebrates 100th AGM
Plans for energy store at former power station in Barry approved
Demolition of turbine hall at the former Aberthaw Power Station Takes place
Swapping date night for drysuits at Barry Dock RNLI
13,900 French Rugby Fans fly into Cardiff Airport ahead of Six Nations Fixture
Vale Councillor blasts school funding in the county
Bear Field Skate Park set for major upgrade as part of new Placemaking Plans
New apprenticeship courses in construction to be introduced in Wales