In what police are calling a "tragic accident," a two-year-old Calgary girl died Tuesday after getting her head caught in the power window of an SUV.

"It came about as just a tragic set of circumstances that led to this child passing," said acting Det. Andrew MacLeod Wednesday.

"The young family is completely destroyed by this as you can well imagine. Instead of celebrating the two-year-old's birthday today, they are mourning her tragic loss."

No charges will be laid, he said.

The girl and her six-year-old brother had been left in the Chevrolet Blazer with the engine running as their mother stopped at an office building to run an errand around 9 a.m., Calgary police said.

When the two-year-old, who was in the back seat, started crying, her brother unbuckled her from her car seat. He then fell asleep in the front seat, police said. 

The young girl then began playing with the power windows.

"She climbed up to pop her head out the window, to get some fresh air or whatever," said MacLeod. "But by doing so she lifted her feet up on to the arm rest, subsequently stepping on the button, which released the window to go up." 

Witnesses heard the girl yelling for her mother. When one witness got closer to the vehicle, he realized the girl was trapped in the window, police said.

He freed the girl, placed her back in her car seat and ran to call 911. Police said he had asked someone to check on the girl while he was making the call, but it is unclear whether that happened.

While he was on the phone, the mother returned to the car, not realizing her daughter had been hurt. She thought both children were just sleeping, buckled her daughter into her seat, and drove away.

It wasn't until she dropped her son off at school that she realized her daughter was unresponsive and called 911.

The girl was transported to the hospital and pronounced dead.

An autopsy will be performed to determine the exact cause of death but police say it appears to have been cardiac arrest.

"I think this is one more thing that no one imagined could be possible, a young child dying at their own hand playing with the power window buttons," said Duty Insp. Luch Berti Tuesday. "If the car doesn't have the keys in the ignition, if the car's not running, it's virtually impossible. Let's just all learn something from this."