Animal rights activists who delayed the start of the Grand National also caused delays on the motorways by gluing themselves to the road.
North West Motorway Police said on Twitter: “We have a number of people sat on the M57 at junction 2 northbound – motorway is closed.”
National Highways said traffic was stopped in both directions on the motorway – between junctions one and two – shortly before 5.15pm, but by 6pm the southbound carriageway was reopened and northbound traffic was being diverted via a slip road.
There were delays of more than an hour on the road, which runs from the M62 to Aintree.
Pictures showed protesters wearing pink T-shirts on the carriageway.
Out of 39 runners, 17 horses finished the race with the Sandy Thomson-trained Hill Sixteen suffering a fatal fall at the first fence.
Merseyside Police Assistant Chief Constable Paul White said: “Today, as you’ve seen, there’s been a significant protest in relation to the running of the Grand National.
“This began earlier this morning, there’s been a number of protests outside and then that resulted earlier on today at about 5pm with numerous people trying to incur onto the course, which we, in partnership with the event organisers, and members of the public as well, have managed in the main to stop and and ultimately the event took place – albeit with a slight delay.”
He said protesters tried to access the course from a number of points at the far side of the track.
He added: “The perimeter of the course is four to five kilometres long so you know, that is a significant resource required to try and cover every area of that.
“We put a proportionate policing plan in place and, by and large, we were able to stop the vast majority entering onto the course, a small number did get onto the course, but, very quickly, they were removed, again in partnership with the event organiser, private security and police officers and staff.”
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