Counting continues after Saturday's by-election and on Monday afternoon, Ms McBain led by 746 votes.

She has claimed victory in the NSW seat but hasn't heard from Liberal rival Fiona Kotvojs.

"No early morning phone call just as yet," Ms McBain told the ABC.

"But with most of the votes now counted, we're very confident that Labor will retain the seat of Eden-Monaro."

The Australian Electoral Commission says Ms McBain has 50.41 per cent on a two-party-preferred basis, compared to Dr Kotvojs on 49.49 per cent

The commission must wait until July 17 to allow time for all postal ballots to come in before it declares a result.

Dr Kotvojs is waiting for the official results for the seat while Ms McBain claimed victory on Sunday.

Labor suffered a drop in its primary vote of about three percentage points, which the party puts down to the loss of former MP Mike Kelly's personal vote.

There have been some in the coalition annoyed at the role of NSW Deputy Premier John Barilaro, who briefly flirted with the idea of running as the Nationals' candidate in the seat that overlaps his state electorate.

In the week leading up to polling day, he faced accusations he was undermining the Liberals in order to have a clear tilt at the seat in 2022 - something he denied.

Labor says it received enough Nationals preferences from voters to make a difference to the result.

"The campaign ended the way it began with the other side all arguing and fighting against each other while Kristy McBain had one focus, which was the people of Eden-Monaro, who really have been doing it tough," Opposition Leader Anthony Albanese told Nine's Today program.

Liberal backbencher Andrew Laming said it was never helpful to have anyone other than the candidate taking headlines because it looked like disunity.

"You'd rather not have that happening in a by-election at all - it's not really what he said, just the fact that he was actually talking at all was the problem," Dr Laming told Sky News.

But he said it was difficult to take "big and significant lessons out of results this fine".

Australian Associated Press