The Metropolitan Police is searching for a man believed to pose a risk to the public.
Vasile Coceban, 36, absconded from a mental health facility in north-west London at about 10:30 BST on Wednesday. He is described as white, 5ft 4in, and of average build with brown hair.
Members of the public should not approach him but should call 999.
Images released by the Met show Mr Coceban on the morning he went missing, wearing a purple camouflage hooded top and grey tracksuit bottoms, which he might since have changed.
It is believed he has bought a large black rucksack and new clothing, thought to be a grey tracksuit top and a red t-shirt.
Detectives said it is likely he is still in north-west London, in particular Brent, but he might have travelled to Hyde Park and back again, using the rail network.
Det Supt Andrew Brien said extensive patrols were conducted in the area where Mr Coceban was believed to be, but the police have appealed for help to keep the public safe.
“It is possible that Vasile is sleeping rough or camping in the Kilburn area or nearby. Please check any sheds or gardens and keep your eyes peeled if walking in parks and open spaces.
“It is important we return him to the facility where he is being treated.”
