A large hunting knife was wielded in the face of a shop owner during an armed robbery.
Detective from the Metropolitan Police said the suspect walked into a mini supermarket on Brook Street, Erith, Bexley, on Thursday February 1 and threatened the 45-year-old store owner.
Waving the knife, the suspect demanded cash from behind the counter and emptied the till's contents into a white plastic bag, police said.
As he was interrogating the owner, a woman and child entered the store and both were asked to wait outside.
The suspect went outside, spoke to the woman and boy, then re-entered the store and took eight packets of cigarettes, two canned drinks and some sweets which he handed to the pair before walking off into Northumberland Heath Park.
The suspect is a black man and approximately 5ft 6in tall. He was wearing dark-coloured clothing, including a black Nike tracksuit, scarf, hat and gloves.
Detective Constable Maxine Hudd, investigating officer from Bexley CID, said: "We believe that this could possibly be linked to a number of robberies that have taken place in the Erith area since 15 December 2017.
"Police are appealing for witnesses to this incident, specifically the woman and child, who were outside the shop, or anyone who saw the suspect enter or leave the park."
Anyone with information is asked to call Bexley CID on 020 8284 9146 or Crimestoppers anonymously on 0800 555 111.