The massive military parade that President Donald Trump has long wanted is set to step off from the Lincoln Memorial, with tanks, bands and thousands of troops.

And the biggest question marks are whether it will be overshadowed or delayed by either the weather in Washington or planned protests elsewhere around the country.

Falling on Trump’s 79th birthday, the parade was added just a few weeks ago to the army’s long-planned 250th anniversary celebration.

A happy birthday message to the US military and Trump has come from Israel’s Prime Minister Benjamin Netanyahu, who described Trump as an “extraordinary leader”.

The display has triggered criticism for its price tag of up to $US45 million ($69 million) and the possibility that the lumbering tanks could tear up city streets.

The army has taken steps to protect the streets, including laying metal plates down along the route.

The display of America’s army on Saturday, local time, comes as Trump has shown his willingness to use his fighting forces in ways other US presidents have typically avoided, inviting lawsuits and accusations that he is politicising the military.

He has deployed the California National Guard and US Marines to provide security during Los Angeles protests tied to immigration raids.

It marks the first time in 60 years that a president activated the National Guard on federal orders inside a state without a governor’s permission, and California Governor Gavin Newsom has filed a lawsuit to stop the deployments.

Children pose for a photo with a US Army tank displayed on the National Mall in Washington DC ahead of the US Army’s parade.

Earlier in the week, Trump raised eyebrows during a speech at Fort Bragg when members of the 82nd Airborne Division were directed to stand behind Trump and they booed and cheered during his incendiary remarks, including condemnation of his predecessor, Joe Biden.

The Defense Department has a doctrine that prohibits troops from taking part in political activity while in uniform.

Trump has shrugged off concerns about the parade cost, the rainy forecast and the potential for protests.

“What a day it will be!!!” Trump wrote on his social media site, adding later that he hoped the weather would cooperate but that if it doesn’t, “that brings you good luck. That’s OK too. Doesn’t matter. Doesn’t affect the tanks at all. Doesn’t affect the soldiers. They’re used to it. They’re tough. Smart.”

As for the protests, he warned that “they will be met with very big force”.

The “No Kings” rallies planned in hundreds of cities nationwide are meant to counter what organisers say are Trump’s plans to feed his ego on his 79th birthday and Flag Day.

No protests are scheduled to take place in Washington, DC, however.

With rain expected, there is a chance the parade could be interrupted by thunderstorms, but White House spokesperson Anna Kelly has said the march will go on rain or shine.

The parade fulfils Trump’s desire for a big parade that he tried to get done in his first presidential term after seeing one in France on Bastille Day in 2017.

The army expects as many as 200,000 people could attend the festival and parade, which will include 6169 soldiers and 128 tanks, armoured personnel carriers and artillery, while 62 aircraft fly overhead.

Tens of thousands attend rallies

Protests from New York to Atlanta to Los Angeles on Saturday, local time, ahead of the military parade, have marked the largest outpouring of opposition to Trump’s presidency since he returned to power in January.

All planned “No Kings” protests in Minnesota were canceled following news a Democratic politician had been killed in what Governor Tim Walz described as a “politically motivated assassination”.

People heading into Washington for the parade encountered a massive security presence, with some 30 km of 2.4m-high black fencing, much of it reinforced with concrete traffic barriers, cordoning off streets and surrounding landmarks including the Washington Monument.

—with AAP