An "ambush" on firefighters which attackers filmed on mobile phones was "a new depth" in violence endured by fire crews, a union has said.
Up to 20 youths attacked firefighters as they put out a pile of burning rubbish at Blacks Road in west Belfast at about 2100 BST on Monday.
One firefighter was hit on the head by a large stone from close range. He has since been discharged from hospital.
The FBU's Jim Barbour said the phone filming was "especially sickening".
"It's a new depth in the recreational violence that our firefighters are having to put up with," he added.
Mr Barbour said there was a "copycat" element to the increasing number of attacks on firefighters.
He blamed part of this on a government media campaign which had "backfired".
"We believe that the campaign was wholly wrongly constructed and has led to copycat attacks like the one last night," he said.
He added: "Our great concern is not just that the number of attacks is increasing, but the nature and the severity is also on the increase."
The area fire commander for Belfast, Chris Kerr, said he had "no doubt" that it was a "premeditated ambush".
"We believe the people who set this fire were the same people who called the Fire and Rescue Service and the same ones who attacked them when they arrived," he said.
"While that is reprehensible in itself, a chilling dimension to this is that people were using mobile phones to take photographs and video clips of the firefighters being attacked."
He added: "When you drop a large boulder three feet from the victim onto his head, there can be no other purpose than to cause serious injury.
"It brings a new and frightening dimension to attacks on firefighters."
Northern Ireland Office Public Safety Minister Shaun Woodward appealed to the public to show their full support for the fire service.
"We need the public to stand fully behind everyone who bravely works in our emergency services," he said.
"Last night one of the crew was seriously injured. Anyone who has any
information about the attack, and knows who carried out this disgraceful act, should come forward with that information.
"What happened last night was a straightforward criminal act. It is
particularly repugnant because it was carried out against emergency rescue workers who, every day, are prepared to risk their own lives.
"We must continue to seek ways to make this kind of incident a thing of the past."