About 200 Manchester United fans broke on to the Old Trafford pitch to protest against the Glazer family’s ownership of the club.
The protest took place before United’s home Premier League game against Liverpool, which is scheduled to kick off at 16:30 BST.
The fans were removed from the pitch before some got back on to it later.
There also appeared to be a protest outside the hotel where the United players stayed before the game.
Fans gathered outside the ground and scores of green and gold flares – the colours of United’s first shirts when they were Newton Heath and the original anti-Glazer protests in 2010 – were set off at 14:00.
The protests follow United’s decision, along with five fellow Premier League clubs, to join the European Super League last month before they all pulled out.
Referee Michael Oliver and former United captain Gary Neville were among those whose vehicles were surrounded as they entered the stadium.
There was no trouble and both were allowed through amid much anti-Glazer chanting.
The view from inside Old Trafford
Gary Flintoff, BBC Radio 5 Live producer
In these times it is quite bizarre to see supporters inside the stadium. Fans broke through at the megastore end, many wearing the green and yellow scarves – the colours of United’s first shirts when they were Newton Heath – and many wearing baseball caps with their faces covered.
They chanted for the Glazers to get out of their club and many gathered in front of the Sky Sports presentation platform, chanting towards the pundits. One fan threw a flare in the direction of that platform.
A few fans picked up some chairs and threw them as they made their way on to the pitch, and groundstaff had to remove litter off the pitch.
Five or six fans actually made it down the tunnel towards the dressing rooms. The club tell us that dressing rooms weren’t breached and no fans made it inside, but we saw a young man led out of the tunnel and down the pitch. Fans have now been cleared from the interior of the stadium.
The next tricky moment is when the two coaches arrive, because the suggestion is that the fans will do their very best to make a barrier to stop the teams making their way on site here.