Witnesses described seeing medics giving CPR to three people lying on the ground.
One passerby, Holly Eddleston, told the Standard: “I was on Parsons Green walking my dog when a policeman ran up to us and said to leave the park immediately so that a helicopter could land.
“I walked towards the station, there were lots of police cars and a section cornered off with fabric – apparently somebody being resuscitated.
“Sounds of a girl screaming and crying were piercing.
“All of the roads in Parsons have been closed, including my own. Undercover police are searching the area looking down all drains with torches and helicopters circling also. Extremely sad.”
Another witness wrote online: “Came out of Parsons Green Tube Station 30 mins ago to the aftermath of a stabbing. 3 bodies receiving CPR. Station now shut and road closed.”
Sources report that one person has been killed and two more are injured. There are no information regarding their condition.
It is not being treated as terrorism-related, a Met Police spokeswoman told the Standard.
No arrests have been made.