Paramedics and police were called to a unit complex on Pitt Street in Waterloo following a concern for welfare report for a 45-year-old man at 2am today.

NSW Police Assistant Commissioner Peter McKenna said paramedics arrived on the scene first and then made an “urgent request” for help from police.

McKenna said the man was suffering from a mental health episode and was at first cooperating with emergency crews, with paramedics able to get him into the ambulance with police assistance.

But he soon “became aggressively resistant” to the paramedics and police and had to be restrained.

Paramedics then tried to sedate him and he went into cardiac arrest.

McKenna said he did not know whether he had been sedated or not when he went into cardiac arrest. 

Officers and paramedics tried to revive the man.

He was taken to Royal Prince Alfred Hospital, where he was pronounced dead.

“Police and ambulance were there to help this person,” McKenna said.

“The circumstances of what happened after that will all form part of the investigation, there’s body-worn video that will be part of the investigation.”

“I can say that I’m not aware of any arms (weapons) being used aside from handcuffs.” 

A critical incident investigation team from the State Crime Command’s Homicide Squad will investigate the circumstances around the incident.

The man was known to police. 

The investigation will be subject to an independent review by the Professional Standards Command and will be overseen by the Law Enforcement Conduct Commission.