Dallas warning sirens 'set off by hacker'

A hacker has been blamed for setting off more than 150 warning sirens in the US city of Dallas over the weekend.

The sirens are usually used to warn of extreme weather events such as tornadoes.

"All 156 sirens in the city were activated last night - it does appear at this time that it was a hack," a spokeswoman for the city told reporters.

The noise "woke up a lot of people", she added.

The sirens were activated at 23:42 local time (04:42 GMT) on Friday and lasted for about 90 minutes.

Some posted footage online in which the sirens can clearly be heard.

Technicians for the Office of Emergency Management were eventually able to shut the warning system down and find what they said was evidence that the siren system had been hacked.

"We do believe that the hack came from the Dallas area," a city statement said.

Last year, someone hacked into a number of traffic signs in Dallas and used them to publish jokes. There has been no suggestion that the same people were involved in the sirens incident.