Unable to start sshd daemon "no hostkeys available"

Issue

• Error while connecting through SSH (Putty or Winscp), following errors can be seen in /var/log/messages:

  Feb 23 21:43:54 node1.example.com sshd: It is required that your private key files are NOT accessible by others.
  Feb 23 21:43:54 node1.example.com sshd: This private key will be ignored. 
  Feb 23 21:43:54 node1.example.com sshd: key_load_private: bad permissions
  Feb 23 21:43:54 node1.example.com sshd: Could not load host key: /etc/ssh/ssh_host_ed25519_key
  Feb 23 21:43:54 node1.example.com sshd: sshd: no hostkeys available -- exiting.
  

• sshd daemon fails to start/restart and reports as sshd: no hostkeys available -- exiting.