Facebook has drawn criticism for failing to activate its Safety Check feature immediately after the Brussels attacks.
The tool, which allows users to indicate that they are safe if they are thought to be in an area of danger, had yet to be switched more than an hour after the first reports of explosions at Zavantem airport in the Belgian capital.
With phone networks reportedly congested in Belgium, many have demanded that the feature be switched on immediately to help people track the whereabouts of friends and family members.
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As of at least 10.30am, the feature had been turned on and users were marking themselves as safe.