The Metropolitan Police issued an urgent warning as phone lines went down for forces across UK.
The Met said many 999 calls were not connecting and advised people to call 101 in an emergency.
They tweeted: “Due to a technical fault that is impacting a number of police forces, many 999 calls are not connecting.
“Until further notice, please call 101 in an emergency.
“Please ONLY call in an emergency and please wait until later to make any 101 non-emergency calls.”
South Wales Police and Greater Manchester Police also shared the same post on Twitter.
The post said the fault had impacted a “number of forces” – but did not specify which ones.
Hampshire Police tweeted: “Our colleagues at BT are having significant systems issues this morning and as things stand the 999 system would appear to be down.
“Please call 101 only if you have an emergency.”
West Yorkshire Fire and Rescue said: “Please contact 101 in an emergency while issues with 999 call persists. BT are working to rectify these issues.”
The 999 system has been restored at around 10.00AM as the Met shared on Twitter that anyone needing police assistance can call 999 as usual.