🇬🇧 UK: 111 (Option 2)
🇺🇸 USA: 1-800-273-8255
🇨🇭 Switzerland: 143
🇸🇪 Sweden: 90101
🇦🇺 Australia: 000
🇧🇪 Belgium: 112
🇨🇦 Canada: 911

More countries: https://en.m.wikipedia.org/wiki/List_of_suicide_crisis_lines

The Samartians: https://www.samaritans.org

Thanks to @michellesanver's tweet.