"... blood started pouring and my brother didn't have any way to punch back. He just lowered his head trying to protect himself. He punched him on the face continuously and very heavily."
Mr Han said his brother had told him the man was so angry that he looked like he wanted to kill him.
The man left when Mr Han started yelling for help and two other cleaners working at Centreplace Shopping Centre heard his screams and ran to his aid.
Spotless Group public affairs manager Kerrina Lawrence said two staff cleaning in the mall administered first aid and waited until ambulance and police arrived.
Police city shift manager Senior Sergeant Rupert Friend said it appeared the man had gone to the shopping mall to find somewhere to sleep after being asked to leave the men's night shelter.
Mr Han said his brother was yesterday recovering at home. The right-side of his face was swollen and cut and he could not open one eye.
He had been a cleaner for many years and this was the first time something like this had happened.
The entrance to the Tower Building is locked in the evenings and can be accessed with swipe cards.
Centreplace manager Greg Wills said it was possible the man got in when someone else swiped their card to enter.
A 27-year-old man, Vutha Meas, appeared in Hamilton District Court yesterday charged with unlawfully being in a building and injuring with the intent to injure. He was remanded in custody and was due to reappear this morning.