The circumstances of the stampede Saturday at the famed Love Parade festival in Duisburg in western Germany were still not clear even hours after the chaos, but it appeared that some or most of the 18 had been crushed to death.
Authorities also suggested that some of the people killed or injured might have attempted to flee the crowd by jumping over a barrier and falling several meters (yards). Witnesses described a desperate scene, as people piled up on each other or scrambled over others who had fallen in the crush.
"The young people came to celebrate and instead there are dead and injured," said Chancellor Angela Merkel. "I am horrified by the suffering and the pain."
Criticism quickly fell on city officials for allowing only one entrance to the grounds of a hugely popular event that drew hundreds of thousands of people to dance, watch floats and listen to DJs spin. German media said 1.4 million people attended but that figure could not be immediately confirmed.
The founder of the Love Parade, Matthias Roeingh, known by the name Dr. Motte, blasted the planning for the event, saying "one single entrance through a tunnel lends itself to disaster. I am very sad."
City officials chose not to evacuate the site, fearing it might spark more panic, and many people continued partying, unaware of the deaths.
Emergency workers had trouble getting to the victims, hampered by the huge crowds. The area was a hectic scene, with bodies lying on the ground and people milling around or attending to them. Rescue workers carried away the injured as techno music thundered in the background.
Local media reported that the cell phone system in Duisburg broke down temporarily and frantic parents trying to reach their children instead drove to the scene to look for them.
However, most streets downtown were blocked by police and the highways leading to the city were jammed. Several media outlets also reported that rescue helicopters had problems taking away the heavily injured because there was not enough space for them to land.
Authorities believe the panic might have first been sparked outside the tunnel when some revelers tried to jump over a barrier and fell, said Wolfgang Rabe, the head of the crisis unit set up by Duisburg city authorities.
Police commissioner Juergen Kieskemper said that just before the stampede occurred at about 5 p.m. (1500 GMT, 11 a.m. EDT), police closed off the area where the parade was being held because it was already overcrowded. They told revelers over loudspeakers to turn around and walk back in the other direction before the panic broke out, he said.
Eyewitness Udo Sandhoefer told n-tv television that even though no one else was being let in, people still streamed into the tunnel, causing "a real mass panic."
"At some point the column (of people) got stuck, probably because everything was closed up front, and we saw that the first people were already lying on the ground," he said.
"Others climbed up the walls and tried somehow to get into the grounds from the side, and the people in the crowd that moved up simply ran over those who were lying on the ground."
Another witness, a young man who wasn't named, told n-tv the tunnel became so crowded that people began falling. "It got tighter and tighter from minute to minute and at some point everyone just wanted out," he said. "People were just pushed together until they fell over."
Duisburg city officials decided at a crisis meeting to let the parade go on to prevent more panic and another stampede, said city spokesman Frank Kopatschek.
It is the worst accident of its kind since nine people were crushed to death and 43 more were injured at a rock festival in Roskilde, Denmark, in 2000. That fatal accident occurred when a huge crowd pushed forward during a Pearl Jam gig.
The Love Parade was once an institution in Berlin, but has been held in the industrial Ruhr region of western Germany since 2007.
The original Berlin Love Parade grew from a 1989 peace demonstration into a huge outdoor celebration of club culture that drew about 1.5 million people at its peak in 1999. But it suffered from financial problems and tensions with city officials in later years, and eventually moved.
The website of the Love Parade - whose motto this year was "The Art of Love - went black on Saturday night, with words in white saying:
"Our wish to arrange a happy togetherness was overshadowed by the tragic accidents today. ... Our sincere condolences to all the relatives and our thoughts are with all of those who are currently being taken care of."
Gera reported from Berlin. Associated Press Writers Geir Moulson and Kirsten Grieshaber contributed to this report from Berlin.