US politicians have reached an "agreement in principle" to avoid another government shutdown.

Officials say they have reached a deal to fund the government through the fall, which would resolve ongoing immigration disputes and stave off a partial government shutdown set to recommence this weekend.

All that remains is for President Donald Trump to sign the deal.

Speaking after a meeting of negotiators, US Republican Senator Richard Shelby did not give an outline of the deal but said staff will work out the details.

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The negotiators had worked into the night in hopes of striking a deal on funding border security through September 30.

If pollies don't act, hundreds of thousands of federal workers will be furloughed for a second time this year.

Negotiations had broken down over the weekend over funding for immigrant detention beds and physical barriers that would be funded along the US-Mexico border.

The politicians wanted to reach an agreement to allow time for the legislation to pass the House and Senate and get signed by the President by Friday, when funding for the Department of Homeland Security and several other federal agencies expires.

Earlier hundreds of government personnel descended on the Texas border town of Eagle Pass to block passage of migrants who arrived via "caravan", parking vehicles and roaming the banks of the Rio Grande river.

About 1800 caravan migrants arrived this week, travelling in groups from South America, and arriving at Piedras Negras in Mexico, a river city and border town separated from the US by the Rio Grande river.

Trump agreed on January 25 to end a 35-day partial US government shutdown without getting the $US5.7 billion ($8.46b) he had demanded from Congress for a long- promised wall along the border with Mexico.

Democrats oppose a wall, calling it ineffective, expensive and immoral. Instead, a three-week spending deal was reached with congressional leaders to give politicians time to resolve their disagreements about how to address border security.

Trump, who said in December he would be "proud" to shut the federal government over border security, took a different tack on Monday.

"It's up to the Democrats," he told reporters at the White House when asked whether the government was headed toward its second shutdown of the winter.