An eight-year-old girl and a 38-year-old man are dead following an early morning complaint of domestic assault, Thunder Bay police report.

When emergency responders were called to an apartment in the 400 block of Donald Street West, just before 3 a.m., they reportedly found a woman had been the apparent victim of a domestic assault by an ex-boyfriend.

When police arrived, it was discovered the woman's daughter had a critical injury. The girl was transported by ambulance to Thunder Bay Regional Health Sciences Centre, where she was pronounced dead. The girl's mother had non-life-threatening injuries.

donald street thunder bay police

Thunder Bay police say an assault at a Donald Street residence in Thunder Bay has turned into a homicide investigation. (Nicole Ireland/CBC)

The man, 38, had fled the scene before police arrived.

A few hours later, at about 7:30 a.m., police received a call regarding a suspicious vehicle which was parked at the end of Wharton Road. The vehicle matched the description of the suspect's vehicle in the Donald Street homicide.

Thunder Bay Police contained the area surrounding the vehicle and attempted to communicate with the man inside. The standoff ended just after 11:30 a.m. and the man was arrested. The man was taken by ambulance to hospital with injuries police said he appeared to have sustained prior to his arrest.

A short time later, the man was pronounced dead.

wharton road thunder bay

Just after 11:30 a.m. on Monday, a man was arrested in the Wharton Road area and taken to hospital by ambulance. Police said he had injuries that appeared to have occurred prior to his arrest. The man later died. (Nicole Ireland/CBC)

The province's Special Investigations Unit — a civilian agency responsible for investigating situations involving police and civilians that have resulted in a death, serious injury, or allegations of sexual assault — has been called in to investigate the circumstances surrounding his death.

The identity of the eight-year-old girl is not being released at this time.