The US Senate voted on Saturday to advance to the next step of a $1tn infrastructure package, an important procedural stage towards passing the key legislation after months of negotiations between Joe Biden and a bipartisan group of senators.

In a 67-27 vote demonstrating broad support, senators agreed to limit debate on the legislation, which represents the biggest investment in decades in America’s roads, bridges, airports and waterways.

Eighteen of the Senate’s 50 Republicans voted to move forward on the legislation, with senators John Cornyn and Deb Fischer backing the package for the first time.

But the timing for passage by the congressional upper chamber remained unclear early on Saturday afternoon, as lawmakers prepared for expected votes on amendments and worked behind closed doors to reach an agreement that would allow the Senate to complete its work on the legislation quickly.

“We can get this done the easy way or the hard way. In either case, the Senate will stay in session until we finish our work,” the Democratic New York senator and majority leader Chuck Schumer said in a floor speech before the vote. “It’s up to my Republican colleagues how long it takes.“

If it passes, the Senate will send the bill on back to the House of Representatives for further consideration.

Biden tweeted his support ahead of the vote, saying the “once-in-a-generation investment in our nation’s infrastructure” would create good-paying jobs refurbishing America’s roads, bridges, water systems and electrical grid.

“We can’t afford not to do it,” the president said.

Vice-President Kamala Harris visited Capitol Hill on Saturday to bolster support for the legislation.

The chamber’s top Republican, the minority leader, Mitch McConnell, also signaled his support for the bill before voting for it.

“Republicans and Democrats have radically different visions these days, but both those visions include physical infrastructure that works for all of our citizens,” McConnell said in a speech. “The investments this bill will make are not just necessary; in many cases, they are overdue. Our country has real needs in this area.“

Lawmakers have been unable to reach agreement on a final batch of amendments that could speed up consideration, leaving the Senate to consider amendments on a piecemeal basis under rules that require legislation to move forward in stages through a series of procedural votes.

With the consent of all 100 senators, the chamber could move through amendments to passage later on Saturday. But without such an agreement, passage could take until Monday or Tuesday.

Asked how long the process could take, Senator John Thune, the chamber’s No 2 Republican, told reporters: “Depends how long we spend staring at each other.”

The Infrastructure Investment and Jobs Act is the first of Biden’s two infrastructure packages. The administration and congressional leaders will soon turn to a second, $3.5tn package that is expected to draw only Democratic support.

Senator Lisa Murkowski of Alaska, a moderate Republican, who voted to advance the $1tn package on Saturday, said her state needed money for a variety of developments including installing water systems in remote villages without running taps for hand-washing during the pandemic. But as one of the negotiators who has sat down with Biden at the White House over the bill, she also wants to demonstrate that lawmakers can unite.

“I’m really worried that everybody believes that we’re as dysfunctional as we appear to be, and so to prove otherwise, it’s kind of important,” she said. “The Senate needs some demonstrated acts of bipartisanship.”

The bipartisan package is funded by repurposing other money, including untapped Covid-19 aid, and other spending cuts and revenue streams.

An analysis of the bill from the Congressional Budget Office drew concerns, particularly from Republicans. It concluded that the legislation would increase deficits by about $256bn over the next decade.

The House is in recess and is expected to consider both Biden infrastructure packages when it returns in September.