The victim – believed to be a man in his 20s – was rushed to hospital but his condition is not yet known.
A cordon has been placed around the scene blocking off nearby bars and restaurants, while several police cars have blocked off the road.
Images from the scene show an air ambulance after it landed in nearby football pitches to attend to the incident.
And unconfirmed reports suggest a gang on motorbikes armed with a machete were involved in the attack.
One Twitter user said: “Hearing there were people on motorbikes with machetes going after people in Russell Square.. if you have loved ones round there check on em!”
Another added: “Massive incident at Russell Square! HUGE @metpoliceuk presence!”
One onlooker tweeted: “Footy finished early due to paramedic heli landing on pitch. Stabbing 200yards away. 20 odd youths chased. Brunswick square gardens.”
It is believed to have occurred in the Brunswick Square Gardens area, near Russell Square tube station.
One man has been arrested on suspicion of Grevious Bodily Harm (GBH). Read More