As the US Government shutdown edges towards being the longest in history, the impact it has been having on American families is becoming more overwhelming.

The Government has been shut down since December 22 and President Donald Trump has warned it could drag on for months or even years if he doesn't get funding for a border wall.

On Wednesday he walked out of a meeting with the Democrats to try and end the shutdown, saying it was a "total waste of time".

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But the longer it drags on, the more Government employees are being impacted. And it could get worse.

FBI agents are among those working without pay

An estimated 420,000 federal employees are working without pay, including the FBI. ( Reuters: Peter Morgan, file photo )

Not all Government departments have been shut down. About three quarters of them remain open, including the Department of Defence and the Postal Service, which have secure funding.

But about 800,000 employees from the departments of Homeland Security and Transportation, among others, have been furloughed or are working without pay.

They work at the following departments:

The Interior Department — including the National Park Service

The Interior Department — including the National Park Service The Commerce Department

The Commerce Department The US Department of Health — including the US Food and Drug Administration and the US Department of Health and Human Services

The US Department of Health — including the US Food and Drug Administration and the US Department of Health and Human Services Department of Agriculture

Department of Agriculture Transportation Department

Transportation Department NASA

Sorry, this video has expired Angry furloughed government workers protesting shutdown

About 420,000 federal employees have had their work declared essential and are working without pay, including the Federal Bureau of Investigation (FBI), Transport Security Administration (TSA), staff at the State Department and the Department of Homeland Security, and other federal law enforcement officers.

Private contractors working for many government agencies are also without pay, along with private companies that rely on business from federal workers or other consumers — such as national park visitors.

Employees are struggling to pay mortgages and bills

Some people are applying for loans to get by. ( Reuters: Joshua Roberts )

Employees on unpaid leave have begun to face financial problems as the shutdown continues.

As the ABC's North America correspondent Conor Duffy put it: "Losing one pay cheque means reworking the budget."

There have been reports of people calling mortgage companies hoping to extend their loans or delay payments while some have had to leave bills unpaid.

Others have been forced to cut back on food bills or electricity while some employees are seeking unemployment insurance or applying for loans to help them out while the partial shutdown continues.

Single parent Leisyka Parrott, a Bureau of Land Management employee in California said she has been staying home as much as she can to reduce her expenses on petrol.

"It's scary," she said. "I do live pay cheque to pay cheque."

National parks, monuments are overflowing with rubbish

Trash collection, restroom and road maintenance have been halted. ( AP: Andrew Harnik )

The National Park Service, under the umbrella of the Interior Department, is currently operating with a skeleton staff.

Under its contingency plan, some parks may be accessible although the park service is providing no visitor services such as restrooms, facility and road maintenance and trash collection.

Others have been closed completely, along with the Smithsonian museums and the National Zoo in Washington, which receive national government funding.

Campgrounds have begun closing because of sanitation issues.

Some volunteers have worked to clean up sites, according to media reports, and some states and other localities have also pitched in funding to keep parks operating.

Airport queues are getting longer and flights could be delayed

Travellers have already reported longer checkpoint lines. ( Reuters: Lucas Jackson )

The TSA has acknowledged more screeners are calling in sick at some airports.

This is because most airport screeners earn between $US26,000 ($36,200) and $US35,000 ($48,700) a year, according to TSA, which is far less than many other government employees. This makes them more vulnerable if they don't get paid.

Travellers have already reported longer checkpoint lines, including at LaGuardia Airport in New York.

President of the National Air Traffic Controllers Association Paul Rinaldi said safety is not being compromised but that capacity to manage traffic could be reduced if the shutdown worsens an existing shortage of controllers.

That could lead to flight delays, he said.

Briefly people couldn't get married in Washington, DC

People hoping to get married could not obtain licences. ( Flickr: Piet Theisohn )

The courthouse office that issues marriage licenses in Washington, DC has been closed because the local courts are funded by the Federal Government.

It meant that people hoping to get married couldn't obtain licences.

But on Tuesday the DC council unanimously passed emergency legislation, valid for 90 days, allowing Mayor Muriel Bowser to issue marriage licenses in the interim.

The economy will soon be impacted

No economic data is being published. ( REUTERS: Brendan McDermid )

Economists have already warned that a prolonged shutdown could hit the US economy, with some analysts having already downgraded economic growth predictions as a result.

That's because the shutdown is starting to impact private companies working with Government and outside of it.

Meanwhile, work at the Securities and Exchange Commission (SEC) has also been halted with "only an extremely limited number of staff".

It's meant that any current investigations are now on hold and companies applying for stock offerings to raise cash or applications to consider merger and acquisition filings are not being reviewed.

On top of this, the Department of Commerce's Bureau of Economic Analysis and Census Bureau is not publishing economic data during the shutdown.

That includes figures on gross domestic product, inflation, personal income, spending, trade and new home sales.

This could eventually have an impact on the Federal Reserve and their interest rate decisions, since the data is used to see how the economy is tracking and whether monetary intervention is required.

ABC/wires