Police raced to Vicarage Road, Watford, at 3.17am on Wednesday following reports that “several people had sustained stab wounds”.
It is understood that the three involved are known to each other.
Armed officers and a dog unit were among those to be called to the scene, Hertfordshire Police said.
The road remains closed this morning while police continue to investigate.
A police spokeswoman said: “At 3.17am today (July 3) police were called to Vicarage Road, Watford following a report of an incident where several people had sustained stab wounds.
“Officers attended alongside the ambulance service.
“Three people were taken to hospital. Armed officers and a dog unit were sent to the scene to support local officers due to the nature of the incident.
“The road is currently closed and members of the public are asked to avoid the area as police continue their investigation.”
Police are appealing for witnesses and for anyone else with information, the spokeswoman added.
She said: "Enquiries into the incident are continuing at this time, however it is believed to have been an isolated incident between people who are known to each other.
"There is no perceived ongoing threat to members of the community."
