A serious crash involving a large truck and a bicycle on Highbury Avenue near Brydges Street has left a cyclist with life-threatening injuries.

Emergency crews were called to the scene around 12:40 p.m. and police quickly closed northbound Highbury.

Witnesses like Jose Belfast-Kum describe a horrific scene after the crash.

"All we heard is this woman scream and then we came to the front and we saw saw her leg and it was just severed."

Those nearby did their best to assist the cyclist, using a belt as a tourniquet and applying pressure to the wound.

Police say a woman in her 40s was transported to hospital following the collision and remains in critical condition.

London police Const. Amanda Pfeffer says, "It's not clear entirely at this point in our investigation whether the driver of that truck knew that he was involved in a collision, but we certainly need to speak with him and establish what occurred."

Late Wednesday afternoon, police Tweeted that they had located the driver and vehicle involved with the help of witnesses, but said the investigation was continuing.

The roadway was re-opened around 3:30 p.m.