A cyclist struck by a car on Carlton street has been sent to hospital with head trauma.

Toronto police responded to a call at 7:13 p.m. The driver stayed on scene and the man struck was sent to St. Michael's Hospital.

Paramedics say a man in his 30s was transported in life-threatening condition. The driver was not injured, according to Toronto police Sgt. Dave Sammut.

Toronto police Sgt. Dave Sammut says the collision occurred after the cyclist got in front of the car. Both were going eastbound on Carlton. (CBC)

"It appears that the motor vehicle and the cyclist were both travelling eastbound on Carlton," said Sgt. Sammut. "At some point the cyclist got in front of the motor vehicle, we're not exactly sure how that occurred, and as a result the cyclist and the motor vehicle got in a collision."

Sammut said he did not know if the cyclist was wearing a helmet.

Mateusz Lawrynowicz was instructed to apply pressure on the cyclist's injured arm after calling 911. (CBC)

Eyewitness Mateusz Lawrynowicz called 911 and was instructed on how to give the cyclist medical attention for injuries to his arm.

"He was bleeding pretty badly," he said. "When I was on the phone with [911] they told me to put pressure on his arm and there was blood everywhere."

Parts of Sherbourne Street and Seaton Street have been closed as police investigate.

Traffic re-construction and detective units are on scene.