Bystanders are taking selfies at the site of the Sydney siege

And people are not happy with them.

As the Sydney hostage crisis unfolds, social media users have been called 'messed up' and 'insensitive' for taking selfies at the scene and posting them online.

Several bystanders - mostly tourists and shoppers - took photos of themselves standing in Martin's Place near the Lindt Chocolate Café where a gunman has taken at least 15 people hostage.