Over 1,000 British holidaymakers have attended the Portugal Invasion festival in Albufeira.
But the party did not end in peace – instead a mass brawl broke out in a bar which sparked large-scale riots and violence.
Local police fired shots into the air to disperse crowds of British tourists after disturbances in the Algarve resort.
Around 50 anti-riot police were sent to the Oura strip after ugly scenes sparked by a bar fight during a party at which all the guests dressed in white.
Portugal Invasion is a festival in the Algarve that has led to widespread riots and violence
GNR officers had to fire at least twice into the air to quell unrest before making four arrests.
Two policemen and two Britons were injured in the violence, which happened during the seven-day festival due to end today.
Yesterday British holidaymakers caught up in the violence accused the police of overreacting, although local business owners said some of the estimated 1,000 tourists believed to have travelled to Portugal for the festival had acted disgracefully during their stay.
The tense situation has prompted concern over whether the holiday destination is safe to visit.
Portugal Invasion – 1,000 British holidaymakers descended on the Algarve for the festival
Portugal’s iconic Algarve is extremely popular with British holidaymakers
The FCO assures travellers most of the 2.6 million UK visitors to Portugal each year have a trouble-free stay
But the Foreign and Commonwealth Office (FCO) hasn’t updated its travel advice in light of the violence.
The FCO assures travellers most of the 2.6 million UK visitors to Portugal each year have a trouble-free stay.
While terrorist attacks “can’t be ruled out” in Portugal, the country’s terror threat is low compared to many other popular European holiday destinations.
According to the FCO, crime rates are low but pickpocketing in tourist areas can sometimes be violent.
Travellers are also warned of fatal forest fires which have been raging in the Pedrogão Grande area of central Portugal.
The FCO said: “Other smaller fires have also been reported elsewhere in the country due to high temperatures. Forest fires are highly dangerous and unpredictable; check with local authorities if you’re considering travelling to the affected areas.”
Britons can continue to use EHIC cards in Portugal to access discounted medical care while on holiday.
Your passport must be valid for the duration of your stay.