Large sections of empty seats could be seen in the Liverpool end in the lead-up to kick-off as they struggled to make their way into the ground due to the chaos outside.
Some supporters were filmed climbing the gates to enter the stadium as police used tear gas in a desperate attempt to curtail the chaos.
Speaking on BT Sport, former Liverpool and Real Madrid striker Michael Owen said: “It is so sad and obviously everything has to be military precision out there.
“We don’t know what’s gone on, but it is sad to hear. You just hope everyone is safe.”
And ex-Manchester United defender Rio Ferdinand added: “We pray for people’s safety. You come to football to be entertained.”
Meanwhile, BBC journalist Nick Parrott is outside the stadium and told Radio 5 Live: “I have just been pepper-sprayed for the first time in my life. I have been to the Champions League final before and I have never been pepper-sprayed before.
“I was outside Gate Y which has been opening and closing repeatedly over the last hour and a half but nobody has been going through. The security staff on the other side advanced and sprayed pepper spray.
“I have seen 10 fans trying to climb over fences. Gate Z is open but there does not seem to be any movement going in. I have never seen this sort of chaos at any match I have been to in a personal capacity.
“The Liverpool fans are trying to move themselves back from these gates to try and get in but the authorities seem to be doing nothing. I came to get into the stadium at seven o’clock.
“I got through the outer perimeter where there is crushing. I came round in good time and it was quite clear that we were not going to get in before nine o’clock.”