Support poured in from police forces across Ontario after five officers were killed and six wounded in downtown Dallas in what has been described as an "ambush style" shooting Thursday night.

Messages of condolences for 5 slain Dallas Police officers were met with outrage over U.S. gun laws and concerns over racial tensions as the hashtags #Dallas and #PrayforAmerica trended on Twitter.

Five Dallas police officers have been killed and six others suffered gunshot wounds after a targeted attack in the city's core Thursday night.