US President Donald Trump hailed the strength of America as thousands of children enjoyed the time-honoured tradition of rolling hard-boiled eggs across the manicured lawn in his back garden.

Welcoming families to the annual White House event, which was dampened by intermittent rain, Mr Trump said: "This is the 139th Easter Egg Roll. Think of it, 139.

"And we will be stronger and bigger and better as a nation than ever before. We're right on track."

His wife Melania, their son Barron, 11, and the Easter Bunny joined him on a balcony overlooking the expansive lawn before they went downstairs to join some of the 21,000 people at the biggest social event of the year at the White House.

Before joining the festivities with his family, Mr Trump also thanked his wife for "working on this for a long time to make it perfect".

There had been some speculation about whether the Trumps would be able to pull off a successful "egg-stravaganza". Planning seemed to get off to a late start, with the Trumps taking longer than in previous years to announce Monday's date.

Both Mr Trump and the First Lady have been slow to fill White House jobs, and at least one regular egg roll vendor took to Twitter, the president's favourite social medium, to remind the White House that a deadline for ordering the wooden eggs that are given out as souvenirs was approaching.

The egg rolling event, which dates back to 1878, was smaller than previous years - down from the 35,000 people who got tickets last year - but retained such activities as a reading nook where messages can be sent to US troops.

"As we renew this tradition, thank-you for joining us," the First Lady said.

Moments later, Mr Trump blew a whistle three times, each time sending groups of youngsters scurrying to deftly use a wooden spoon to manoeuvre their dyed egg several yards across the finish line.

The Trumps and their son also joined children at a table to make cards to send to US service members.

Mr Trump's older sons Donald Jr and Eric, and their wives, and daughter Tiffany also attended.

In the reading area, Mrs Trump read Party Animals, a story about celebrating differences written by television personality Kathie Lee Gifford.

Costumed characters roaming the grounds included Elmo from Sesame Street, Dr Seuss's Cat in the Hat and Teenage Mutant Ninja Turtles.