An estimated 200,000 people have been taking part in the annual Darkness into Light event in aid of Pieta House.
The walk and run through the early hours of the morning, into dawn, is now in its 10th year.
Walks have been organised in 180 venues across Ireland and several more are taking place around the world.
It is expected to raise more than €4m for the charity which offers counselling for those affected by suicide.
One runner spoke about why he took part in this morning's events.
He said: "The biggest killer for men under 45 is suicide.
"I think it's an enormous issue across the world particularly in Ireland and it's something that isn't talked about."
Another said she was joining the event to raise awareness about depression in young people.
She said: "I think depression affects some many young people today and it's a great thing to raise awareness.
"The number of people who die by suicide in this country, particularly young people is humongous."
- Digital Desk