The US president has declared a public safety emergency as he promises to tackle crime and homelessness in the nation's capital.

On Saturday, Trump said the nation’s capital has become “one of the most dangerous cities anywhere in the World.” Last week he threatened to deploy the National Guard to D.C. and, as he has on several occasions since he was inaugurated in January, suggested that there should be a federal takeover.

U.S. President Donald Trump said on Monday he was deploying 800 National Guard troops to Washington and temporarily taking over the city's police department, an extraordinary assertion of presidential power in the nation's capital.