Barcelona ultras reportedly smashed a window of Atletico Madrid's team bus during their hostile arrival at the Nou Camp. 

With the Catalan giants looking to overturn a four-goal deficit in their Copa del Rey second leg on Tuesday evening, riot police were deployed to guard against disorder as raucous fans gathered outside the stadium. 

Footage shared on social media shows hordes of supporters lining the streets, waving red flares as baton-wielding officers watched on.

In one video, a policeman had to kick away a flare after it landed on the ground before the Atletico team bus arrived. 

According to Marca, a group of 'local hooligans' then began launching missiles upon the arrival of Diego Simeone and his players.

The Spanish outlet added that one of the objects 'hit its target' and 'ended up breaking the window of the team's official team bus' amid the chaos.

It was claimed that Simeone and his players were made an 'easy target' after entering through a separate gate from the Barca team, where most of the Catalan police were reportedly stationed.

In comparison, the home fans greeted their own bus with fireworks and chanting of 'Yes we can! Yes we can!' in a reference to the daunting task ahead.

Barca were humiliated by Atletico with a 4-0 loss at the Metropolitano last week, but put on a pre-match display for the return leg on Tuesday featuring fireworks in a bid to gee-up the crowd for a potential comeback.

'We are four goals behind and we have to make the impossible possible,' boss Hansi Flick had said in his press conference on Monday.

'That is the objective. It's not easy. However, we will not give up. It is important to keep a clean sheet, but we must believe in our strength and that we can achieve it. You must always believe. For example, in each half we need to score two goals.'

In the end they fell just short of levelling the tie, winning 3-0.