PROSECUTORS have filed a tougher charge against the former police officer at the centre of the George Floyd case, as well as charging three other sacked officers.

Derek Chauvin, who was seen on video pressing his knee into Floyd's neck, has seen his charge upped from third to second-degree murder.

The three other officers at the scene – Thomas Lane, J Alexander Kueng and Tou Thao – were charged for the first time with aiding and abetting second-degree murder and second-degree manslaughter. All four were fired last week.

The new charges were sought by Minnesota attorney general Keith Ellison, who called the protests unleashed by the death "dramatic and necessary" and said Floyd "should be here and he is not".

"His life had value, and we will seek justice," said Ellison, who cautioned that winning convictions would be hard and said that public pressure had no bearing on his decisions.

Benjamin Crump, a lawyer for Floyd's family, called it "a bittersweet moment" and "a significant step forward on the road to justice".

He said Ellison had told the family he would continue his investigation into Floyd's death and upgrade the charge to first-degree murder if warranted.

It came after A local medical examiner ruled the death a homicide.

Nationwide, more than 9000 people have been arrested in connection with the unrest which erupted after Floyd’s death.

At least 12 deaths have been reported, though the circumstances in many cases are still being established.