DUISBURG: Authorities were searching for clues Sunday as to what touched off a sudden stampede at the Love Parade dance party in Duisburg, western Germany that killed at least 18 people.

Around 15 others were seriously hurt and dozens more sustained lighter injuries as a crush occurred in or around a tunnel leading to the day-long open air festival, attended, officials said, by some 1.4 million revellers.

"According to our current information, 18 people have died and around 80 people have been injured at the entrance to the festival grounds," the mayor of the host city Duisburg, Adolf Sauerland, in a statement.

The exact causes of the disaster were unclear and it was not certain whether foreigners were among the dead at the event, which attracts thousands from all around the world.

Police initially said the crush happened in the tunnel itself but an official from Duisburg, a city of 500,000 just north of Duesseldorf, said others also died on steps leading towards it.

Most revellers remained unaware of the incident and continued dancing and listening to the music long afterwards as authorities kept a lid on the news to avoid another panic.

Eyewitnesses said the horrific scenes were "unimaginable."

One young female partygoer told Die Welt daily: "Everywhere you looked, there were people with blue faces."

"My boyfriend pulled me out over the bodies, otherwise we would both have died in there. How can I ever forget those faces. The faces of the dead."

Another witness told the NTV rolling news channel that several people had fallen to the ground and had been trampled underfoot.

"Some people were on the ground while others were climbing up the walls," said the witness, Udo Sandhoefer.

Police officers and security officials tried to get into the tunnel "but it was already too full," he added.

"People kept trying to get into the tunnel for about 10 minutes, then realised what had happened and turned around," he said.

Another 18-year-old witness named Marius told the Bild daily: "There was no way of escaping. There was a wall of people in front of me. I was scared I was going to die."

Panicked friends and family sent a raft of messages on Twitter in a bid to locate missing partygoers.

Chancellor Angela Merkel said she was "aghast" at the catastrophe.

"In these difficult hours, my thoughts are with the relatives of the victims. They have my sympathy and my condolences."

"Young people came to party. Instead, there was death and injury. I am aghast and saddened by the sorrow and the pain," she said in a statement.

President Christian Wulff said: "Such a catastrophe that has caused death, sorrow and pain during a peaceful festival involving young people from many countries is dreadful."

Shock turned quickly to anger as partygoers criticised organisers for only allowing one entrance through the tunnel to the festival.

There was "simply nowhere to get out" of the area around the tunnel, one survivor told WDR television.

Focus magazine quoted the founder of the Love Parade, who goes by the name of Dr Motte (Dr Moth), as saying: "The organisers are to blame ... they showed not the slightest responsibility for people."

The influential mass circulation daily Bild asked on its website: "Why did the police let people carry on the party?"

Sauerland defended the security and vowed to hold a comprehensive enquiry.

"In the run-up to the event, we worked out a solid security plan with the organisers and everyone involved," he said.

"The investigations that have already been launched must uncover the precise course of events."

BDST: 0900 HRS, July 25, 2010