The victim died at the scene in Ilford just before 9pm, and no arrests have yet been made.
Officers were called to Cranbrook Road outside Ilford Station at 8.48pm to reports of a stabbing.
A man in his 20s was pronounced dead at the scene about half an hour later.
Zamirullah Stanikzai, 21, who works in a phone shop close by, said he saw two men brandishing knives.
“I saw people running up and down the station when I went out,” he said.
“I saw people running up and down the station when I went out”
Zamirullah Stanikzai, eyewitness
The Metropolitan Police said in a statement: “An urgent investigation has been launched after a fatal stabbing at 8.48pm in Cranbrook Road
“The victim, in his 20s, died at the scene. No arrest made at this early stage. We’re working to confirm ID and inform family. Anyone with info pls call 101 ref 7377/feb26.”
Ilford South MP Mike Gapes tweeted: “Shocked and saddened to hear of the fatal stabbing of a young man this evening.”
Tuesday night’s stabbing was the sixth in just nine days in the capital.
A schoolboy was knifed outside a train station in west London in front of horrified commuters.
An air ambulance was spotted arriving at South Ruislip station and the victim was taken to a major trauma centre.
Two hours later, an 18-year-old man was rushed to hospital after being knifed in Romford, east London.
While last week, Bright Akinleye, 22, died in the lobby of a luxury hotel after being stabbed in the street near Euston Station.
Glendon Spence, 23, also died last week after being stabbed at a youth club in Brixton in the south of the city.
Three people were also stabbed on a packed Oxford Street in central London nine days ago.
There were also knife attacks in Southwark, south London, Wood Green in north London, and Tower Hamlets in east London in the past week and a half.