Flags are being flown at half mast above Scottish government buildings to remember six people killed when an out-of-control refuse truck ploughed into Christmas shoppers in Glasgow.
Another 10 people were injured, including the driver, after the lorry swept along a crowded pavement in the city centre yesterday, knocking pedestrians down "like pinballs", according to one horrified onlooker.
Scottish police identified the victims as Jack and Lorraine Sweeney, aged 68 and 69, who are thought to be the grandparents of a third victim, 18-year-old student Erin McQuade.
The three other victims were Gillian Ewing, 52, Jacqueline Morton, 51, and Stephenie Tait, a 29-year-old primary school teacher.
Queen Elizabeth expressed her condolences, saying in a statement: "This sad event is made even more difficult as it comes at Christmas time."
The Church of Scotland organised a prayer service for the victims on Tuesday and opened a book of condolences at St George's Tron church, a short walk from the scene of the tragedy on George Square.
"This morning it's a city with a broken heart," First Minister Nicola Sturgeon, who visited the scene of the crash, told BBC radio.
Floral tributes brought by members of the public were placed near the scene of the accident, including one with a card reading simply "Why?"
Police said it appeared to have been a tragic accident but Chief Superintendent Andy Bates said they were still investigating and asked for anyone with photos or videos of the incident to send them in.
Glasgow was back in mourning just over a year after a police helicopter crashed into a bar in the city on November 29, 2013, killing eight people and injuring more than 30 others.
Reverend Alastair Duncan, who led the prayer service, said there was "a definite sombre note in Glasgow, compared to yesterday when it was boisterous and festive and the streets were crowded".
The city's Celtic football club said it would hold a minute of silence before its next match on Saturday, while Glasgow-born Scottish tennis star Andy Murray tweeted his condolences.
The local authority bin lorry veered over a distance of around 300 metres, only stopping when it crashed into a hotel near Queen Street station.
The driver survived and was taken to hospital.
Eyewitness reports suggested he was slumped at the wheel, raising speculation that he may have had a heart attack.
Four of the injured have been discharged from hospital, leaving six people including the driver, still undergoing treatment, officials said.