A Louisville police officer has been charged with three counts of "wanton endangerment" in connection with the March shooting of Breonna Taylor, a 26-year-old black woman, in the US city.

Judge Annie O'Connell announced the charges brought by a grand jury against Brett Hankison, one of three police officers involved in the fatal shooting.

Ms Taylor, an emergency room technician, was shot dead in her apartment when three plain clothes police officers executing a "no knock" search warrant burst in late at night.

Her death fuelled weeks of anti-racism protests in Louisville, Kentucky, and became a nationwide rallying cry for the Black Lives Matter movement for police reform.

Ahead of the announcement, Louisville Mayor Greg Fischer announced a 72-hour curfew for the city beginning at 9pm local time, with exceptions for those going to work or to seek medical treatment..

Ms Taylor's boyfriend, who was in bed with her, grabbed a gun and exchanged fire with the officers. He later said he thought they were criminals.

The officers, who had not activated their body cameras as required, shot Ms Taylor multiple times, killing her. A police sergeant was wounded.

The city of Louisville settled a wrongful death suit with Ms Taylor's family for $12 million last week and a grand jury has been looking into whether any charges should be filed against the officers involved in the raid.

The grand jury is to present its findings to Jefferson County circuit judge Annie O'Connell later this afternoon.

A state of emergency has been declared by the mayor in Louisville, which has a population of 600,000, with much of downtown closed to traffic.

Some downtown business owners have boarded up their shops in anticipation of potential unrest sparked by the grand jury decision.

Louisville police chief Robert Schroeder said the authorities would not tolerate any "violence or destruction of property".

"We are prepared to meet any challenge we may face," Mr Schroeder said, calling for demonstrators to protest "peacefully and lawfully".

The civil settlement with Ms Taylor's family reflected the public pressure and emotion surrounding her death, which came about two months before that of George Floyd, a black man who was killed by a white police officer in Minneapolis.

Mr Floyd's death triggered protests across the US against racial injustice and police brutality.

Kentucky state and local authorities have pledged to implement reforms intended to prevent incidents similar to the botched raid in which Ms Taylor was killed.

Officer Hankison has been fired and the other two officers were suspended. The city has also banned "no knock" warrants.

The case has sparked international outrage, and earned celebrity attention.

Oprah Winfrey paid for billboards in Kentucky demanding justice for Mr Taylor and US Open champion Naomi Osaka wore a face mask bearing Ms Taylor's name during her run for the title.