Guelph Police Const. Jennifer Kovach, 26, was a vibrant, gregarious and dynamic woman with a sense of adventure, Police Chief Bryan Larkin said.
"I cannot say enough about what an incredible human being she was," he said at a press conference.
"There are no words to express our sorrow. There are no words to express our sadness."
Kovach was responding to a call when her cruiser hit a Guelph Transit bus shortly after 12:30 a.m.
The bus had no passengers at the time and the driver, who had only minor injuries, provided "significant care" to Kovach, but after firefighters managed to extract her from her cruiser and she was taken to hospital, she was pronounced dead, Larkin said.
There was a light snowfall at the time and investigators are looking into whether road conditions were a factor, Larkin said.
"Const. Kovach was responding to a call for service in assisting another officer with a frontline call," he said.
"Regrettably, we believe (she) lost control of her cruiser and crossed the centre line and struck a transit bus."
Kovach, who loved her dogs and riding motorcycles, was at the start of a promising career, fulfilling her childhood dream to be a police officer, Larkin said.
"I think that from a perspective of the chief, one of the greatest challenges is to see somebody with so much potential, with so much energy, taken from us so soon," he said.
"If you talk to the members of her platoon...Jennifer didn't come to work, she came to make a difference in the city of Guelph. She came to touch the people of the city of Guelph and she came to actually give back."
Prime Minister Stephen Harper used his Twitter account to send his sympathies to Kovach's loved ones.
"Tragic news out of Guelph," the tweet said. "Condolences to the friends and family of Constable Jennifer Kovach."
Kovach had been with the force for four years.
Her family likely instilled in her the value of public service, Larkin said. Kovach was the daughter of Gloria Kovach, a longtime city councillor and former president of the Federation of Canadian Municipalities.
Mayor Karen Farbridge expressed her condolences to the Kovach family in a statement Thursday morning.
"There are no words that can adequately express our sorrow over their tragic loss," she wrote.
"We also recognize this is a very difficult time for our Guelph Police Service who have lost a member of their service. We would like to express our gratitude for their brave service, and assure them that Constable Kovach will always be remembered for her sacrifice to keep our community safe."
Kovach is the third officer to die in the line of duty in the history of the Guelph Police Service, and the only one since 1964.
Ontario Premier Kathleen Wynne said she was deeply saddened to hear of Kovach's death.
"She was so young, with such a promising career ahead of her and her presence will be missed on the job and throughout her community," Wynne said in a statement.
"Ontario owes a debt of gratitude to Const. Kovach and all of our police officers, who do so much to serve and protect the people of this province."
— By Allison Jones in Toronto.