Police were called to an incident in Glebe Road, Hamilton, on Monday morning where a man, reportedly under the influence of ice, hacked off his own finger.

An eye witness driving past the man about 7.45am pulled over after seeing he was in distress.

The man then hacked off his own finger with a broken bottle, threw it in an adjacent garden, crossed the street and walked up Glebe Road toward the corner of Hassall Street.

The witness, who dialed triple-0, said she believed the man could have been on ice.

"I was driving to work and saw the guy, I got out of the car because I saw him harming himself," the witness said.

"[He was] sitting down, I actually saw him doing a cutting motion where his arms were.

"They were in front of his legs as if he was leaning over his legs and cutting himself.

"I thought at first he was self harming so I tried to stop him, not thinking he was on anything [drugs].

"I got onto the emergency and was explaining everything that was going on at the time.

"This included the man going back to hacking at his finger with the piece of glass and I could see that it was slowly coming off.

"The man then had his finger hanging by the skin, I could see bone and I could see blood spurting out like it does in the movies when an arm gets chopped off.

"He then grabbed the hanging part and yanked it off.

"It was really awful, I couldn't believe it.

"He was inconsolable."

Police and ambulance arrived about 8am.

The witness said police were forced to taser the man twice before he could be subdued.

"The police came very quickly and the man did not want to go with them - the police had to chase him," the witness said.

The pinky finger of the man's right hand had been severed at the first knuckle.

Witnesses looked for the fingertip but it was not found.

Police took the man to John Hunter Hospital with an ambulance escort.

The incident is being investigated.