By 5.30 p.m. yesterday all bus services along the Shankill had been suspended, and the RUC had announced that it had requested the assistance of the British army. This was only the second-time such assistance had been requested in Belfast since September 1998.
This turn of events followed an afternoon of serious loyalist feuding in which two men were shot dead at lunchtime, and offices used by loyalist groups were attacked.
The killings happened shortly after 12.30 p.m. when at least eight shots were fired by a gunman at the two victims, Mr Jackie Coulter and Mr Bobby Mahood, who were sitting in a blue Range-Rover outside a bookmaker's shop on the Crumlin Road.
The road, in the north of the city, is part of what used to be known as "murder mile". With the loyalist Shankill Road meeting the nationalist Antrim Road and Ardoyne areas, it was a fertile hunting-ground for sectarian killers. Yesterday, however, it was Protestant killing Protestant.
It was raining heavily as the killer approached and opened fire, killing Mr Coulter instantly. Mr Mahood was taken to the nearby Mater Hospital with a stomach wound from which he died a few hours later.
About an hour after the shooting, there was a gun attack from a passing car on the offices of the Ulster Prisoners' Aid organisation on the Shankill Road. This group supports UDA prisoners, and its offices are also used by Mr John White, a leading member of the Ulster Democratic Party, the UDA's political wing, and by Johnny Adair, the UDA commander on the Shankill. One man was slightly hurt in the attack.
Retaliation came swiftly as a crowd of around 20 UDA supporters moved 200 yards down the Shankill Road and attacked an office of the Progressive Unionist Party, the political wing of the UVF, at around 2 p.m.
The crowd attempted to shatter the office's armour-plated front windows with hammers, and shots were fired. When the crowd failed to enter the building, they set fire to it. Firemen prevented the flames spreading to neighbouring properties.
As it became clear that the feud was spreading, many shops on the Shankill Road closed for the day. One shopkeeper was less than surprised. "It's been brewing up for years," he said.
As reports began to come in of armed UDA men on the streets, extra RUC officers were brought in. They emerged from their armoured Land-Rovers with assault rifles to begin searching estates in the area.
Just after 2 p.m. two men were arrested and weapons and ammunition seized.
In another incident, police fired two shots at Malvern Street, off the Shankill. There were no reports of any injuries.
Meanwhile, a man was arrested in connection with the recovery of a firearm and ammunition at Lisburn Road, Belfast, last night. The RUC has not linked the incident to the ongoing loyalist feud in the city.