Violent protests over the death of a black man in police custody rocked a Minneapolis neighbourhood for a second straight night as angry crowds looted stores, set fires and left a path of damage that stretched for miles.

The protests that began late Wednesday and stretched into Thursday were the most destructive yet since the death of George Floyd. He was seen on video gasping for breath during an arrest in which an officer kneeled on his neck for almost eight minutes.

In the footage, George pleads that he cannot breathe before he slowly stops talking and moving.

The U.S. Attorney’s Office and the FBI in Minneapolis said Thursday they were conducting “a robust criminal investigation” into Floyd's death and making the case a priority.

The announcement came a day after President Donald Trump tweeted that he had asked an investigation to be expedited.

The FBI had already announced that it would investigate whether Floyd’s civil rights were violated.

The officer and three others were fired Tuesday.

On Wednesday, Minneapolis Mayor Jacob Frey called for him to be criminally charged.