Officers from the Major Collision Investigation Unit were working with the understanding the 83-year-old woman was cycling into Yackandandah when the heavy vehicle travelling in the same direction attempted to pass her.

The incident occurred just after 7.30am, with police closing Isaacs Avenue, and a team from MCIU arrived around 2pm.

"Police are investigating the circumstances surrounding a serious collision involving a cyclist and a truck in Yackandandah this morning," a spokeswoman said.

"Investigators believe the cyclist was riding along Isaacs Avenue around 7.40am when she lost control and fell into the path of an oncoming truck.

"The 83-year-old woman was flown to a Melbourne hospital in a life-threatening condition.

"The truck driver, a 63-year-old man, stopped at the scene and is assisting police with their enquiries."

MCIU spent the afternoon at the scene, inspecting the bicycle and focusing on the back, left side of the truck, which was transporting a single power pole.

Officers at the scene said it was not clear how the woman had come off her bike.

An Ambulance Victoria spokeswoman said she was transported via air ambulance to Melbourne in a critical condition after sustaining upper- and lower-body injuries.

Cyclists often use the narrow bridge over Commissioners Creek, which was built circa 1857.

It is part of VicRoad's gazetted B-Double network.

The incident comes as investigations continue into two fatalities that occurred on Sunday.

A female driver in her 70s died after her car left Katandra Main Road in Yabba North about 1pm, impacting a tree.

At 3.30pm, a car was travelling along the Midland Highway in Benalla when the driver lost control.

The car left the highway and crashed into a tree.

The driver and only occupant of the car, believed to be a man in his 70s, died at the scene.

Anyone with information about these incidents should contact Crime Stoppers on 1800 333 000.

Earlier:

An elderly cyclist has been flown to Melbourne in a life-threatening condition after an incident involving a truck in Yackandandah.

A Victoria police spokeswoman said police were looking into the circumstances which led to the serious collision involving a cyclist and a truck.

Investigators believe the cyclist was riding along Isaacs Avenue around 7.40am when she lost control and fell into the path of an oncoming truck.

The incident appears to have occurred on the main bridge into Yackandandah with officers from the Major Collision Investigation Unit currently on scene, inspecting the bike and the oversized heavy vehicle.

IN OTHER NEWS:

The 83-year-old woman was flown to a Melbourne hospital in a life-threatening condition.

The truck driver, a 63-year-old man, stopped at the scene and is assisting police with their enquiries.

Anyone with information or dash cam footage is asked to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au