The attack happened at around 3.50am this morning in Trafalgar Street, Brighton.
Sussex Police said a man was taken to hospital with “significant injuries”.
Officers are searching the area and the force said people can ‘expect to see a heightened police presence while enquiries are ongoing’
Anyone with any information is asked to report it online or via 101 quoting 162 of 09/10.
1. In Pictures: Sussex city street cordoned off as police attend 'serious incident'
In Pictures: Sussex city street cordoned off as police attend 'serious incident' Photo: Eddie Mitchell
2. In Pictures: Sussex city street cordoned off as police attend 'serious incident'
In Pictures: Sussex city street cordoned off as police attend 'serious incident' Photo: Eddie Mitchell
3. In Pictures: Sussex city street cordoned off as police attend 'serious incident'
In Pictures: Sussex city street cordoned off as police attend 'serious incident' Photo: Eddie Mitchell
4. In Pictures: Sussex city street cordoned off as police attend 'serious incident'
In Pictures: Sussex city street cordoned off as police attend 'serious incident' Photo: Eddie Mitchell