The US Senate has voted to extend the deadline for Australians to vote in its presidential election until mid-October, despite widespread opposition.

The move has been welcomed by Democrats and some Republicans, but critics say the move will make it harder for the party to win in November.

The Senate voted in favour of extending the deadline by a two-thirds majority on Thursday, after senators approved a motion to delay the vote.

The motion was approved by a voice vote, with nine senators voting against it.

The vote comes just two weeks after Democrats used their majority in the Senate to defeat President Donald Trump’s nomination of Alabama senator Jeff Sessions to be US attorney general.

Mr Sessions was also rejected as the next attorney general by the Senate, and is expected to face a tough confirmation fight in a November vote.

How voting goes down The Senate vote came after Democrats and Republicans agreed on amendments to the US constitution to allow senators to cast ballots for president if they were not in the chamber for the time being.

The amendments were put forward by Senators Joe Manchin, Joe Donnelly, Heidi Heitkamp and John Barrasso, who all support extending the voting period for Americans who were unable to vote because of health or other reasons.

They were supported by Senator Ron Wyden, a Democrat from Oregon.

Democrats say they are concerned about the impact of the Senate vote on turnout.

“The Senate has been in session for over six weeks, yet still has no votes to pass a law to make it easier for Americans to vote,” Senator Donnelly said in a statement.

“As a result, millions of eligible voters are being left without a chance to vote.”

Senator Barrasso said it was “a matter of basic fairness and respect” to ensure voters had an opportunity to cast their ballots.

“We are going to continue working to ensure that the American people have the same opportunity as the Senate is,” he said.

“Our work in the past few weeks has been to ensure there are no votes that will impede the ability of the American voters to have an accurate vote count.”

A bipartisan group of senators also called on the Senate and the House of Representatives to pass legislation that would prevent the extension of the deadline.

“There is no need for this Senate extension because the American public has a right to participate in the democratic process,” Senator Manchin said in an emailed statement.

The US Supreme Court is expected in mid-November to rule on whether states must post an online ballot guide before voters can cast their ballot.

The group of US senators and representatives is asking for the US government to provide funding to fund a tool to help states implement their own online voting guides.

The senators also say they will use the extra time to look at whether states should be able to use a pre-election poll that was conducted on election day.

“If states choose to use pre-elections as a means of pre-counting their vote, that could affect the outcome of the election,” Senator Barraces said.