A memorial service for the 150 victims of the last month's Germanwings plane crash was held today at Cologne Cathedral.

German Chancellor Angela Merkel and German President Joachim Gauck were among the 1,500 members of the congregation, which also included around 500 relatives of the passengers who died in the crash in the French Alps on March 24.

President Gauck said during the service that on the day of the crash "something was destroyed that can never be healed again in this world".

Archbishop of Cologne, Caridnal Rainer Maria Woelki and the president of the Protestant Church of Westphalia, Annette Kurschus led the ecumenical service.

Cardinal Woelki told mourners that "mere words are too weak to console".

"But dear sisters and brothers, the fact that we are all here and the fact that so many people are now connected with us... that shall give you consolation," he added.

Across Germany today, flags have flown at half-mast. Screens were erected outside the cathedral for crowds to watch outside, and the service was broadcast on German television.

Candles were lit on the steps of the altar representing each of the victims, most of whom were German and Spanish.

Co-pilot Andreas Lubitz is thought to have deliberately crashed the plane. It has emerged that he had a history of depression and had been signed off work numerous times, including for the day of the crash.

The head of Lufthansa, Germanwings' parent company, Carsten Spohr also attended the service. Staff from the two airlines who attended the service were told not to wear their uniforms out of respect for the grieving families.