One eyewitness described the vehicle knocking people down "like pinballs" as it veered out of control over a distance of around 300 meters (about 1,000 feet), only stopping when it crashed into a hotel.
"Sadly six people have died as a result of the George Square major road incident," read a tweet on the Scottish police force's official account.
Police superintendent Stewart Carle told reporters at the scene that people were killed over "a number of sites."
He said the driver, who reported by some British media to have slumped at the wheel and perhaps to have suffered a heart attack, was being treated in hospital.
An investigation was under way to establish exactly what had happened, police said.
"The bin lorry just lost control. It went along the pavement, knocking everyone like pinballs," eyewitness Melanie Greig told Sky News.
"People were trying to run out of the way but when something was coming out behind them like that, how can they run out of the way?" she said.
She added: "There was noise, bangs, screams and everything. It was just horrific."
The rubbish truck, owned by Glasgow City Council, mounted the pavement and hit the first pedestrian outside the Gallery of Modern Art on Queen Street at about 2:30 p.m. (1430 GMT), police said.
It struck several more as it continued at speed for another two blocks, crashing at the Millennium Hotel on George Square, near Queen Street station.
Emergency services cordoned off the normally bustling area in what is Scotland's biggest city.
The incident took place the day after a driver with psychiatric problems in the French town of Dijon ploughed into pedestrians, injuring 13.
'Sad day for Scotland'
Scottish police said there was nothing "sinister" about the Glasgow incident, calling it an accident.
"It is a road traffic collision with multiple fatalities," Carle said, adding: "It does not look to be a criminal or deliberate attack."
The accident happened near the Scottish city's main shopping hub, where shoppers filled the streets just three days before Christmas Day.
Residents began leaving floral tributes at the scene, and a note attached to a bunch of pink roses read "To all those who lost their lives and witnessed this horrible tragedy."
The accident occurred just over a year after another tragedy in the city in which ten people died when a police helicopter crashed onto the roof of a pub.
Prime Minister David Cameron said he was being kept informed of developments.
Scotland's First Minister Nicola Sturgeon called it a "sad day for Glasgow and Scotland" and urged anyone who was in the area at the time of the accident to contact their loved ones.
"My thoughts are with everyone involved in this tragic incident, and especially with the friends and families of the six people who lost their lives," she said in a statement.
source: interaksyon.com
