Place the child in a safe place where it cannot be harmed.
It is more important to keep calm than to stop the crying. Talk calmly. Tell the child that you need a break to retain control.
Intense crying can make you so stressed that it's hard to think clearly. To get a break from it, you need to leave the room for a few minutes.
Breathing exercises can calm you down and soothe negative thoughts and worries. See examples of techniques in tip 6.