Authorities in Munich have asked all people in the city's urban areas to stay at home, avoid public places where possible, and remain vigilant. They've also called for people to refrain from posting sensitive information about police operations on social media, in case it aids the attackers.

"Keep calm, pay attention to the announcements we make and to serious news statements, and trust the Munich police. We are proceeding on the assumption of a terror attack, in terms of the fact that we are responding with intense efforts and extensive measures. If it turns out that the background is different, then we will have put lots of measures in place and the worst case scenario is automatically covered," said Marcus Da Gloria Martins, Munich Police Spokesman.