Lowell police are searching for a couple after an unleashed pit bull attacked another pit bull and its owner Wednesday night.

The attack, which happened at the corner of 10th and Myrtle streets at about 9 p.m., left Killian Minch and his 5-year-old pit bull, Blue, bloodied.

Minch said the pit bull, which was about twice the size of his dog, was extremely aggressive, attacking without warning.

“I started punching the other dog as hard as I could, maybe like three or four times,” he said. “I started kicking it instead, and it was just totally unphased by what I was doing.”

After biting his dog’s front leg and left ear, he said the pit bull turned toward him, biting his forearm.

“I felt totally helpless,” he said. “I had blood all over my hands; she was drenched in blood.”

Minch said he tried to talk with the dog’s owners, but they took off.

“That was my biggest problem,” he said. “I don’t understand why a dog that was so big and clearly so powerful — why it wouldn’t be on a leash.”

Minch said he and his dog received medical treatment, including a rabies vaccine.

There is a leash law in Lowell.

Police said they’re searching for a silver Honda SUV, but they don’t have a plate number.