In the minutes leading up to kick-off, stewards lined the walkway separating the 3,800 Roma supporters situated in the second tier of the East stand and the United supporters.

But the travelling Italian fans were stunned into silence as Sir Alex Ferguson’s United turned the quarter-final tie on its head by winning 7-1, and 8-3 on aggregate.

Fighting broke out just outside the ground two hours before kick-off on Sir Matt Busby Way.

Police moved in quickly to try to break up the trouble and calm the situation.

Despite their efforts, the tension between the fans appeared to grow, with Roma fans hurling a firework into a crowd of United supporters.

One eyewitness said there was a stand-off between hundreds of United and Roma supporters, with glass and plastic bottles being thrown.

Before the match started, two Roma fans who had tickets for the game said they were too scared to go inside the stadium for fear of potential harm after the game.

Father and son Alessandro Pinci, 53, and Matteo Pinci, 24, criticised Old Trafford officials for not letting the Roma supporters into the ground early.

Alessandro Pinci said: “We have been here since about 5pm waiting to get in. I do not understand why we were not allowed to go in early before the United fans arrived.

We just had to stand there and shield ourselves as the bottles came flying at us.

“We were put in too much danger by being left outside the ground so late before the kick-off.”

Matteo Pinci said: “This is not football. We do not want to go inside and watch the game because if we happen to win the tie then it will be war outside afterwards.”

The first leg in Rome last week saw fans involved in skirmishes, while Italian police charged United supporters with batons, a move condemned by the club who accused them of handing out “indiscriminate beatings”.

Roma, who led 2-1 from the first leg, brought 3,800 fans with them to Manchester and a high police presence was deployed for tonight’s return match amid a tense atmosphere.

A statement released by Greater Manchester Police said: “Officers patrolling at Old Trafford ahead of the Manchester United versus Roma match this evening have been required to deal with a number of small and isolated incidents.

“The incidents are being dealt with as they happen and are being resolved quickly.

“Some arrests have been made in order to maintain the peace at the ground.

“At this stage there are no reports of anyone injured.”

Tension grew between both sets of fans outside the ground about 30 minutes before kick-off as Roma fans were subjected to searches for weapons as they lined up to enter the stadium.

Police formed a cordon to separate the two sets of supporters as home supporters began throwing bottles and missiles at the Italian fans.

One Manchester United fan broke the cordon and was swiftly grappled to the ground by at least four officers.

Police took out frightened children and parents who were in tears as the missiles rained down on them.

A stand-off ensued outside the front entrance of Old Trafford as a heavy police presence created a no-man’s land about 30 metres between the Roma fans waiting to get into the stadium and the United fans who were congregating outside the Megastore.

Police were steadily gaining control of the situation but the odd bottle still continued to be thrown into the Roma section.

Police tried to hold the opposing fans apart as they queued to get into the ground.

Press Association journalist Neil Lancefield said about 30 United fans charged a media group standing in the no man’s land between the two sets of supporters.

He said: “They just ran into us – we were between them and the Roma fans. We just pegged it towards the stadium.”

Riot police forced the United supporters away from the stadium, he added.

The stand-off ended as police moved along the home supporters into the ground and away from the last few Italians waiting to gain access into the stadium.

The outside of the stadium on Sir Matt Busby Way was strewn with smashed bottles, cans and other debris as the tensions finally appeared to die down.

A line of about 100 officers remained outside the front entrance in preparation for any violence after the end of the game.

Upon entering the ground, the Roma supporters were situated in the second tier of the East stand.

While the police believed none of the Italian club’s hardcore fans would travel, an ’ultras’ banner was clearly displayed, albeit upside down.