A handcuffed man is on the run after he escaped from police at Wollongong Hospital on Thursday evening.

Jason Rees, 43, was arrested by police on Thursday in relation to firearm and assault offences.

Officers took him to Wollongong Hospital to be assessed. At about 6pm, despite being restrained, police say he ran off.

An extensive search was launched involving uniformed police and the dog squad, but after several hours he has not been found.

Police have released a public appeal, urging anyone who sees Mr Rees to phone triple zero immediately.

At the time he ran from police, he was wearing a Sydney Roosters football jersey and black shorts.

Police said he is of caucasian appearance, 175 to 180 centimetres tall and weighs 70 to 80 kilograms. He has short, light brown hair and blue eyes.

He has several tattoos, including a southern cross tattoo on his neck, a scorpion on his left leg and a skull on his right upper arm.

"Jason Rees is considered dangerous," police said in a statement. "Anyone who sights him should not approach him."

Mr Rees was involved in a bizarre nude stand-off with police in February 2015, after he stripped off his clothes and asked officers who were trying to arrest him not to shoot him.

He became agitated when he was handcuffed and taken to Wollongong police station, where he threatened to infect officers with AIDS, throw faeces at them and kill them.

Police have established a perimeter near Wollongong Hospital and continue to search.