A police officer was bitten by a dog as he attended an incident in which a man was attacked and badly hurt.
The victim of the assault was left with serious but non-life-threatening injuries in the early hours of yesterday.
A police officer was also taken to hospital after attending the disorder in Thirlmere Gardens, Derriford, Plymouth, at about 1.15am.
He is not thought to be seriously hurt.
Six people were arrested and taken into custody for questioning as police try to piece together what happened.
Force spokesman Inspector Alistair Fry said: "They are helping us with our inquiries regarding quite a nasty assault."
He said it was not immediately clear what had happened.
Police described it as a major incident attended by all three emergency services.