The men, in their 20s, were rushed to hospital after the attack, which forced the store to close for the rest of Saturday evening.
One of the men is in a stable condition, while police await an update on the other.
A witness who was in the store at the time told the Standard: “I was sat in the café with my daughters about 150 feet away when it all kicked off.
“An alarm went off and we didn’t know what was happening, and then the staff took us out the other entrance.
“One of the guys was laying on the display bed in the foyer with a sheet over him, you couldn’t see any blood or anything because they were covering him up.”
A police spokesman said: “Police were called to Bugsby Way, SE10 at 1833hrs on Saturday, 17 August following reports of a fight.
“Officers, LAS and London Air Ambulance attended and found two males aged in their twenties injured.
“The first man was taken to hospital for the treatment of stab injuries. A full condition update awaits.
“A second man also taken to hospital for treatment of a stab injury. His condition is stable.
“A crime scene remains in place. One man has been arrested on suspicion of affray. Enquiries continue.”