Four US states hit by 911 call outages

People in four US states were left unable to make 911 calls on Wednesday night after widespread system issues.

Many services have been now restored after reports that lines went down for call centres across Nevada, Nebraska, South Dakota and Texas.

Federal officials have previously warned that the move to digital systems by emergency services has brought with it the risk of cyber-attacks.

But a cause of last night's problems has not yet been given.

Officers had earlier said they had been able to see when an emergency call was coming from a mobile device, meaning they could phone the caller back.