Officers attended along with the London Ambulance Service and found two seriously injured men, both aged in their early 20s.
Victim 1 was found with stab injuries and a suspected gunshot wound. He was declared dead at the scene at 01:14hrs.
His next of kin have been informed, although formal identification is yet to take place. A post-mortem examination will be held in due course.
Victim 2 was found suffering from stab injuries. He was taken to an east London hospital, where he remains in a serious but stable condition.
The victims were with some friends outside the parade of shops in South Street near the junction of Scotland Green Road at 00.34 hours when the attack took place.
Four suspects approached the victims from the direction of Curlew House, which is behind the shops. They were all dressed in dark clothing, wearing hooded tops with the hoods pulled up.
Detectives from the Met’s Homicide and Major Crime Command are investigating.
Detective Chief Inspector Andy Partridge, who is leading the investigation, said: "This was a totally unprovoked attack on the victims and their group, with the level of violence used being utterly deplorable.
"The suspects arrived together coming from the direction of Curlew House. They fled together along an alleyway to the side of the Oasis Academy, heading towards Sandhurst Road, passing the allotments and industrial estate.
"Whilst the attack itself only took minutes to carryout, I want to hear from members of the public who may have seen them in the area before the attack or afterwards when they fled towards Sandhurst Road. Any fragment of information could assist the investigation. Please do not assume that we already have your information."
There have been no arrests and enquiries continue.
Anyone who witnessed anything suspicious, or has information that may assist the investigation should call the incident room on 020 8358 0300 or Crimestoppers anonymously on 0800 555 111. You can also tweet police via @MetCC.