The Green Party has dropped its court case seeking a state-wide recount of Pennsylvania's November 8 presidential election.

The party wanted to explore whether voting machines and systems had been hacked and the election result manipulated but party-backed voters who filed the case could not afford the million-dollar bond ordered by the court by 5pm on Saturday, lawyers said.

The decision came two days before the court hearing, but Green Party-backed efforts to analyse election software in scattered precincts are continuing.

Party presidential candidate Jill Stein spearheaded a recount effort in Michigan, Pennsylvania and Wisconsin, where Republican Donald Trump won narrowly over Democrat Hillary Clinton. Mr Trump and the Pennsylvania Republican party had opposed the recount.

Now Stein has vowed to bring her fight for a recount of votes cast in Pennsylvania in the U.S. presidential election to federal court.

"The Stein campaign will continue to fight for a statewide recount in Pennsylvania," Jonathan Abady, lead counsel to Stein's recount efforts, said in a statement.

Saying it has become clear that "the state court system is so ill-equipped to address this problem," the statement said "we must seek federal court intervention."

The Stein campaign said it will file for emergency relief in the Pennsylvania effort in federal court on Monday, "demanding a statewide recount on constitutional grounds."

The bond was set by the Commonwealth Court of Pennsylvania a day after representatives of President-elect Donald Trump requested a $10 million bond, according to court papers.

The court gave the petitioners until 5 p.m. local time on Monday to post the bond, but said it could modify the amount if shown good cause. Instead, Stein's campaign withdrew.

"The judge's outrageous demand that voters pay such an exorbitant figure is a shameful, unacceptable barrier to democratic participation," Stein said in a statement. "No voter in America should be forced to pay thousands of dollars to know if her or his vote was counted."

Stein said she planned to announce "the next step" in the recount effort on Monday at a previously scheduled news conference at Trump Tower in New York City.

She said recounts already under way in some Pennsylvania counties would continue. The state's election commission had approved recounts in 75 precincts where voters requested one, but refused to allow a full forensic audit of voting machines.

Even if all the recounts were to take place, the overall election outcome would not likely change. The race is decided by the Electoral College, or a tally of wins from the state-by-state contests, rather than by the popular national vote.

Trump surpassed the 270 electoral votes needed to win, with 306. Recounts would have to flip the result to Clinton in all three states to change the result.

In the popular vote, Clinton had more than 2.5 million votes over Trump, the independent Cook Political Report said.

