Queensland Police were called to an apartment complex at Kangaroo Point in Brisbane shortly before noon on Friday after the discovery of a body.
Officers cordoned off the entrance to an underground carpark where a garbage truck was parked, after the body was reportedly found inside a bin.
It was the third sudden-death investigation in Queensland within 24 hours.
Just after 3.30pm on Thursday, an 84-year-old man was found unresponsive at a home in Surat, 450km west of Brisbane.
Southern Region Assistant Commissioner Matthew Vanderbyl said other people at the home began driving the man to the hospital a short distance away, such was the advanced state of his medical distress.
''On the way to hospital, they were met by the ambulance and CPR was commenced … and the gentleman was then subsequently transported to the hospital in Surat,'' he said.
The man, who was a long-term resident of the town of 400 people, died shortly after 5pm.
''We've moved to inquire into this matter quite intensively to try and establish what has happened,'' Mr Vanderbyl said.
A post-mortem examination was being conducted on Friday afternoon, and the outcome would be the key point in police inquiries, he said.
Police were interviewing people who were at the home to piece together their movements.
The property and the car had been declared as crime scenes but the assistant commissioner said this was because the death was unexplained.
In the third incident, neighbours alerted emergency services to a fire at a home in Bellbird Park, west of Brisbane, at 5pm on Thursday.
''There were reports of a smell of petrol around the area, so I can tell you that we are very much treating that as a suspicious fire,'' Mr Vanderbyl said.
The intensity of the blaze prevented emergency services from entering the vacant two-storey home and a police guard was placed on the crime scene overnight.
A search of the property on Friday morning led to the discovery of a body.
''When you tragically find the remains of someone in a house, that's a terrible way for someone to perish,'' Mr Vanderbyl said.
''We will do a lot of work over the weekend to try and identify that individual and to advise their family and bring some closure to those people.''
Police were seeking CCTV footage from homes in the area, he said.
