US President Joe Biden signs an Executive Order on the economy on Wednesday in the White House. Photo: AFP

The US Senate on Saturday voted to approve a $1.9 trillion relief package in what President Joe Biden called a "giant step" toward reviving the pandemic-stricken American economy, capping frenzied negotiations and a marathon overnight voting session.

Passed by 50 votes to 49 in a strict party line vote, the sweeping legislation now heads back to the Democratic-majority House of Representatives, where it is expected to be adopted, barring a last-minute setback.

"I promised the American people help was on the way," said Biden in an address from the White House, after the plan was approved along strict party lines.

"Today, I can say we've taken one more giant step forward in delivering on that promise," he said. "It obviously wasn't easy. It wasn't always pretty. But it was so desperately needed."

Even without the progressive priority of a minimum wage increase to $15 an hour, the stimulus bill marks a victory for Biden's Democrats as they put their stamp on the recovery from the COVID-19 pandemic that has killed more than 500,000 people in the US and hobbled its economy.

Top Senate Democrat Chuck Schumer vowed that the bill "will deliver more help to more people than anything the federal government has done in decades." 

The legislation would send out $1,400 stimulus checks to most Americans and allocate $350 billion to state and local governments and $130 billion to schools.

It would also provide $49 billion for expanded COVID-19 testing, tracing and research, and $14 billion for vaccine distribution.

Steny Hoyer, the Democratic majority leader in the House, said the chamber would take up the amended bill on Tuesday, with a view to sending it to Biden for his signature early next week.

The huge bill - the second largest rescue package in US history, after 2020's $2 trillion CARES Act - almost fell apart. 

Senate action was paralyzed for more than 10 hours Friday as Democrats scrambled to retain the support of their most conservative senator, Joe Manchin, who balked at the scale of jobless benefits.

It took a call from Biden and a cut in supplemental weekly unemployment insurance from $400 to $300, among other tweaks, to prevent Manchin from defecting.

The drama served to highlight the growing political muscle of moderates in a deadlocked Senate, where a single swing vote could make or break major legislation.

AFP