A tifo display in the colours of the Palestine flag was evident in the lower half of the standing section well before kick-off and about two dozen sizeable flags were flown in the adjacent section before the teams emerged.
Thousands of smaller flags were evident around the ground when the teams came out.
The displays will inevitably lead to UEFA disciplinary action against Celtic, given the European governing body has already fined the club for fans flying Palestine flags on previous occasions.
The club issued a plea to supporters earlier on Wednesday after the Green Brigade fans’ group encouraged supporters to “courageously fly the flag for Palestine” amid the escalation of the conflict in the Middle East that has claimed thousands of lives.
“We have witnessed death, violence and destruction in the Holy Land in recent weeks, with thousands of people – men, women and children – killed, injured and displaced,” read Celtic’s statement.
“We are witnessing a tragedy of horrendous scale. As it continues, everyone at Celtic prays for all who have been affected.
“We also hope and pray for peace and for humanitarian support to reach those who are in need and in fear.
“Many of our colleagues, supporters, friends and families have been affected by these events.
“Against this backdrop of conflict and pain, sport can promote peace and demonstrate humanity and empathy for all who continue to suffer.”
Celtic added that players and coaches would wear black armbands as a “show of respect and support for all those affected by the conflict” and the club would make a contribution to the International Committee of the Red Cross to “support people affected by the humanitarian crisis in the region”.
The statement added: “The club recognises that our supporters hold personal views to which everyone is entitled. As a club open to all, we all belong at Celtic Park.
“Celtic Park is where we come to support our football club. Recognising this, respecting the gravity of the tragedy unfolding and its impact on communities in Scotland and across the world, and in line with other clubs, leagues and associations, we ask that banners, flags and symbols relating to the conflict and those countries involved in it are not displayed at Celtic Park at this time.”
The Green Brigade, which is currently suspended from getting away tickets by the club, in the wake of incidents at Motherwell and Feyenoord, had earlier announced plans to distribute thousands of flags outside the stadium.
“While it would be easier to distribute flags inside, we are prohibited from bringing the flags into the stadium,” a statement read.
“We respect the right of all fans who wish not to participate in such an action, however equally we ask that the same respect and freedom is afforded to all fans who do.”
In 2016, the Green Brigade raised more than £130,000 in an online fundraising campaign after Celtic were fined nearly £9,000 by UEFA due to fans flying Palestine flags during their 5-2 Champions League victory against Israel’s Hapoel Be’er Sheva in Glasgow.
The money went to medical aid for Palestinians and projects in the Aida refugee camp in Bethlehem, where a football academy was set up bearing the name of Celtic.
Celtic drew the game 2-2 against Atletico.