A judge has temporarily blocked the Trump administration from laying off thousands of federal workers during the government shutdown.

It comes less than a week after the administration confirmed several agencies had begun laying off about 4,000 workers.

US District Judge Susan Illston granted a request by two unions to block layoffs at more than 30 agencies.

During the hearing, Illston said she agreed with the unions that the administration was unlawfully using the lapse in funding, which began on 1 October, to carry out its plans to downsize the federal government.

She also cited a series of public statements by President Donald Trump and the White House's budget chief, Russell Vought, that she said showed explicit political motivations for the layoffs, such as Trump saying that cuts would target "Democrat agencies."

A US Justice Department lawyer said that the unions must bring their claims to a federal labour board before going to court.

The Trump administration is expected to appeal against the restraining order.

On Friday, major departments such as Treasury and Health and Human Services (HHS) confirmed they were issuing notices to employees. Homeland Security, where many of its employees are considered essential, said it would lay off workers at its Cybersecurity and Infrastructure Security Agency.

A filing from the Office of Management and Budget revealed more than a quarter of the cuts were to be made at the Treasury Department, where notices were being sent to approximately 1,446 employees.

HHS was notifying between 1,100 and 1,200 employees, the filing said. The department said later, it was only planning to lay off about half that amount.

The Department of Education and the Department of Housing and Urban Development intended to lay off at least 400 employees apiece, while the Departments of Commerce, Energy, Housing and Urban Development and Homeland Security each planned cuts ranging between 176 to 315 employees, according to the filing.

In response to Vought and Trump's comments about potential firings, two major unions, the American Federation of Government Employees and AFL-CIO, had already filed a lawsuit and then on Friday, asked Judge Illston for an emergency restraining order while the case proceeds.

They argued that implementing layoffs was not an essential service that can be performed during a lapse in government funding.

They also say the shutdown does not justify mass firings because most federal workers have been furloughed without pay.

With the federal shutdown now in its third week, the US Senate again on Wednesday failed to pass a resolution that would reopen the government - the ninth time that resolution fell short.

Republicans, who control both houses of Congress as well as the White House, blame Democrats for the impasse, saying they should agree to pass a "clean" funding resolution that would simply continue current spending levels. Because Republicans hold a slim majority in the chamber, they need a handful of Democratic votes in order to meet the 60-vote threshold to pass the resolution.

Democrats have been fairly unified in holding out for a resolution that addresses health care costs for lower-income Americans that are set to rise soon.