A 25-year-old man has died in Perth's south east, in what is believed to be the third homicide in WA's capital city over a 20-hour period.

WA Police have arrested a 33-year-old man on suspicion of murder, after being called to a home in St James around 4:50pm on Tuesday, where the 25-year-old was found unresponsive.

The man was declared dead at the scene.

Homicide squad detectives are investigating and say the 33-year-old is assisting them with their enquiries.

Deadly 24 hours

It marks the third suspected homicide across Perth from Tuesday morning to Wednesday afternoon.

Around 6:45am on Tuesday, emergency services were called to reports of a critically injured man inside a home in the northern Perth suburb of Hocking.

The 58-year-old was taken to Joondalup Health Campus where he la

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