The world was left devastated after gunman Adam Lanza opened fire at Sandy Hook Elementary School in Newtown, killing 20 children and six teachers.

Now a week on, people are calling for the US to rethink its gun laws so tragedies such as this and the countless others that have occurred will not happen again.

Celebrities such as Selena Gomez, Beyonce, Zooey Deschanel, Jennifer Anisiton and Paul Rudd are part of this video, asking people to act now.

Take a look.

What are your views on this? Should America have stricter gun laws?

Niall Horan, Justin Bieber, Rihanna and celebs tweet their shock and sdaness atb Newtown tragedy