Two men were taken to hospital with head injuries after being assaulted.
Police were called to King Street in Leigh following reports of the incident at around 3am on Friday.
The two men were found with similar head injuries and were taken to hospital.
One has since been discharged after receiving medical treatment while the other is still getting care.
Police shut off part of King Street due to the incident while pictures of the scene showed officers standing outside a former bank.
The building and the neighbouring property had been taped off.
Enquiries are now under way to establish exactly what happened
Greater Manchester Police (GMP) say a number of road closures are in place and have advised motorists to avoid the area.
Anyone with information should contact police on 0161 856 5307, quoting incident number 281 of 27/09/19, or the independent charity Crimestoppers, anonymously, on 0800 555 111.