Pablo Fornals scored in stoppage time to seal a 1-0 win for West Ham in Alkmaar as they progressed to their first European final for 47 years with a 3-1 aggregate victory, but the celebrations were soon paused because of the trouble in the stands.

AZ supporters broke through a fence and attacked the West Ham contingent seated in a reserved section at the AZ Stadium. A brawl ensued in which West Ham players attempted to intervene.

• Report: AZ Alkmaar 0-1 West Ham (agg 1-3)
• How the teams lined up | Match stats
• West Ham fixtures

Police and stewards then arrived on the scene to prevent further confrontation and calm was restored 10 minutes later.

Dutch police issued a statement which read: "So far, no arrests have been made. Our aim was to disperse the crowd and restore order as quickly as possible, in which we succeeded.

"The police will investigate footage of the incidents and try to identify supporters. Arrests may follow from this.

"Together with AZ, the municipality of Alkmaar and the public prosecution service we will evaluate last night's incidents, which we regret having happened. This kind of behaviour has no place in football."

A Met Police statement added: "We are aware of disorder that took place in the stadium following tonight's AZ Alkmaar v West Ham United game.

"As is routine when London sides play abroad, Metropolitan Police officers were present to assist with the wider policing operation.

"Any criminal offences that are identified will be investigated by the Dutch authorities."

UEFA will wait for the reports from the match officials and delegates before deciding next steps.

Moyes: I was worried for my family

West Ham boss David Moyes, whose 85-year-old father was in the crowd, said emotions were running high in the camp after it became clear their families and close one were being targeted.

"We'll need to wait for the dust to settle to see what it is but the biggest problem is that is the area where the players have all their families in," he said.

"That is where the problem came, and a lot of players were getting angry because they couldn't get to see if they were OK.

"What I don't want to do in any way is blight our night. It wasn't West Ham supporters looking for trouble.

"Was I worried? Yeah, my family were there and I had friends in that section. You're hoping they would try to get themselves away from it.

"Security wanted to take me inside, but I had to make sure my players weren't involved."

Match-winner Fornals told Sky Sports News he did not see much of the violence as he tried to keep his team-mates inside away from the trouble but is worried about the welfare of their friends and families.

"I went inside and tried to keep the guys in because we don't need that as players," he said. "I am really concerned about the families of my team-mates, hopefully everyone is OK and the police can do their job and realise who did it.

"It's not great when you are in that beautiful moment and people who isn't in the same moment are trying to use violence against you. We can't do anything else, just try to help the police to realise who did it and pray for the family of my people being good."

Hammers goalkeeper Alphonse Areola added: "When families or friends are coming to the stadium, we don't want to see things like that. They want to enjoy the event and we want to enjoy it with them as well. We were worried about them."

'My girlfriend was shaking'

AZ defender Pantelis Hatzidiakos says his family were left terrified by the aggression as they saw the trouble unfold, condemning the behaviour of the home fans.

"I think it's sad what happened. My family was up there. I have been in contact with them and my girlfriend said they were shaking," the Greece defender told Dutch television.

"I don't even call them supporters. Just stay home if you have such intentions.

"Such a beautiful evening, such a great atmosphere, I really enjoyed it until the final whistle. What happened after that, I find very sad and a pity."

Explained: How the violence unfolded

Sky Sports News reporter Gary Cotterill was at the match on Thursday night:

"Very different sense from yesterday [Thursday] evening. It's very calm and very tranquil here, about 15 miles away from AZ Alkmaar. There were very different scenes last night and it all started with Pablo Fornals' goal which secured a place in the final for West Ham.

"The bench, the coaches and David Moyes were so delighted that they celebrated on the pitch for two or three minutes before the game resumed. And joining those celebrations, of course, because it was so emotional, were the friends and families of the West Ham contingent that were sitting just behind the dugouts.

"The ultras - the hardcore AZ fans - that were behind the goal off to the right saw those celebrations and realised there were West Ham fans in the stadium quite near to them and started to make their way around to that area. There was virtually no stewarding to stop them and there was no riot police or any other kind of police.

"They managed to get to that section and started attacking people in that section. I saw Lucas Paqueta, Said Benrahma, Flynn Downes all jump over from the pitch into the section of the stadium where the friends and families were. They were held back by the stewards and there was a little bit of argy-bargy.

"Playing a captain's role was Declan Rice, who was trying to hold back some of the players, particularly Downes. Aaron Cresswell and Jarrod Bowen were involved in that calming influence as well. Eventually, after quite some time, the riot police did move in. I was surprised about how long it took for them to do so."