Facebook activated its Safety Check feature Tuesday for Brussels following a terror attack in the Belgian capital that killed more than 30 people and injured more than 100 others.

The Safety Check allows Facebook users to let friends know they're safe following a natural disaster or other catastrophic event. When a user is near an event, Facebook will send a notification asking if they're safe. Users can also receive alerts when their friends are marked as safe.

Photos: Brussels terror attacks

The check had been used for natural disasters since it launched October 2014, including earthquakes in Chile and Nepal. Last year's attacks in Paris marked the first time Facebook activated the service for a crisis that was not a natural disaster.

"Over the last few years there have been many disasters and crises where people have turned to the Internet for help," said Facebook CEO Mark Zuckerberg in a statement released when Safety Check first launched. "Each time, we see people use Facebook to check on their loved ones and see if they're safe. Connecting with people is always valuable, but these are the moments when it matters most."

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