Former US President George W. Bush delivered pizzas to his unpaid Secret Service personnel and called for the partial government shutdown to end.

"@LauraWBush and I are grateful to our Secret Service personnel and the thousands of Federal employees who are working hard for our country without a paycheck," he captioned an image showing himself delivering pizzas on Instagram on Friday.

"And we thank our fellow citizens who are supporting them."

The former leader bought his staffers at least six pizzas, according to the Instagram post.

"It's time for leaders on both sides to put politics aside, come together, and end this shutdown," he said.

The message comes as the shutdown, already the longest in history, entered the 28th day on Friday, as President Donald Trump's demand for $5 billion of funding for a border wall has met the harsh political realities of a divided government.

Some furloughed workers have taken to accepting food handouts amid the weeks without a paycheck.

Some 6,000 Secret Service employees are among the 800,000 federal workers not receiving paychecks.

Spokeswoman Catherine Milhoan said on Friday that more than 85 per cent of the agency is continuing to report to work every day.

--IANS