Carers at RSPCA Harmsworth Animal Hospital in Finsbury Park, North London, compared the situation to a 'war zone.'
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Police were called to the scene, where terrified staff had resorted to barricading themselves in, as thugs pelted the centre with explosives.
The youths lined the entrance to the hospital with bins, meaning staff were trapped inside the building and cowered as they hid.
Dramatic camera footage taken by one staff member shows the street alight with fireworks as she said: "It's like something out of a war zone."
Many of the animals were so distressed that they had to be moved elsewhere in the building due, with carers fearing they could be hit by one of the fireworks.
Police are now searching for the perpetrators, and the charity has released a statement.
A RSPCA spokesperson said: "Our dedicated workers at Harmsworth Animal Hospital are trying to continue to care and treat animals during the challenging times of lockdown and they should be able to do this without fear for themselves or the animals.
"Fireworks have been going off in this area during the week upsetting the dogs and animals in the hospital, and staff also reported sparks visible in the branches of the trees close to the hospital.
"We had one particularly horrible incident where fireworks were launched at a police car right outside the hospital.
"This anti-social and dangerous behaviour is obviously unacceptable but, as well as this, lockdown measures this year also mean that very few organised, public displays are likely to go ahead.
"We suspect this will mean people will have their own displays at home instead and we fear that this will result in lots of little displays taking place over a few weeks, spreading out fireworks noise and causing prolonged distress for animals.
"Fireworks are extremely stressful and frightening for lots of animals. But they can also cause very serious injury and even death to some."
RSPCA Harmsworth Animal Hospital provides a home to scores of pet dogs and cats. Many have already endured trauma and neglect.
Attacks from fireworks can carry a fine of up to £5,000 or imprisonment of up to six months.
The Met Police have been approached for comment.
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