Berlin - Germany has held an emotional memorial service for 21 people killed at the Love Parade dance festival last weekend.

At the service, a top state official vowed that authorities would do everything to find out who was responsible for the tragedy.

More than 500 people were injured during a mass panic at the event in the western city of Duisburg.

As a mark of respect, flags across Germany flew at half-mast.

Visibly shaken, the state governor of North Rhine-Westphalia, Hannelore Kraft, said the authorities owed it to the relatives of the victims as well as to the injured and rescue workers to thoroughly investigate what led to the mass panic in a tunnel leading to the festival site.

Chancellor Angela Merkel had broken off her summer holiday to attend the memorial service at the Salvator Church in Duisburg, along with friends and relatives of those killed at the Love Parade festival.

"The Love Parade was like a dance of death," the head of the regional Lutheran church, Nikolaus Schneider, said in his sermon.

"In the middle of a celebration of the lust for life, death showed its ugly face to all of us."

Rescue workers who had helped to look after the victims at the Love Parade site lit a candle for each person who died.

They later carried the candles to the tunnel where the festival-goers were killed and where another service is due to be held this afternoon.

The service at the Salvator Church was broadcast live on German television, and hundreds were watching it on big television screens at other churches and a football stadium in the city.