The Special Investigations Unit is investigating after Toronto police shot and killed a man who was said to be trespassing near a rail line on Friday morning.

SIU spokesperson Jason Gennaro said police officers fired one shot and also deployed a conducted energy weapon around 9 a.m. A 42-year-old man was pronounced dead at the scene.

Gennaro confirmed there was a confrontation between the dead man and police, but said it's unclear if the man was armed.

"The officers were attempting to arrest a man for trespassing under the rail safety act," Gennaro told reporters near rail corridor near Weston Road and Highway 400.

Gennaro said part of the investigation will involve determining if the man had been living in a makeshift shelter in the area.

The SIU is still trying to establish a timeline of events. Police tweeted that they were called to the area around 6:40 a.m., though it's unclear when the Emergency Task Force (ETF) team arrived. Gennaro said the SIU was notified about 30 minutes after the man's death.

ETF officers were also called to the scene, Gennaro said.

The SIU has assigned seven investigators and three forensic investigators to its probe. Anyone who witnessed the incident is being urged to contact the SIU directly.

Ontario's SIU investigates any incident of death, serious injury or alleged sexual assault involving police.