An Australian woman accused of murder denied measuring out a "fatal dose" of poisonous mushrooms on her kitchen scales to kill three elderly relatives of her estranged husband, as she was cross-examined by the prosecution on Thursday.

Erin Patterson, 50, is charged with the July 2023 murders of her mother-in-law Gail Patterson, father-in-law Donald Patterson and Gail's sister, Heather Wilkinson, along with the attempted murder of Ian Wilkinson, Heather's husband.

The prosecution accuses her of knowingly serving the guests lethal death cap mushrooms as part of a Beef Wellington at her home in Leongatha, a town of about 6,000 some 135 km (84 miles) from Melbourne.

She denies the charges, which carry a life sentence, with her defence calling the deaths a "terrible accident."

Under cross-examination on Thursday by the prosecution, Erin Patterson was asked whether a series of photos of mushrooms placed on weighing scales in her kitchen was evidence she had been measuring a "fatal dose" to serve to her lunch guests.

"I suggest that you were weighing these death cap mushrooms so that you could calculate the weight required for the administration of a fatal dose for one person. Agree or disagree?" barrister Nanette Rogers said.

"Disagree," Patterson replied.

Patterson accepted under cross-examination that she had lied to police and medical professionals following the lunch when she was asked whether she had ever foraged for mushrooms or owned a food dehydrator, which was later found in a waste disposal plant containing traces of death caps.

The accused has previously admitted she lied about being diagnosed with cancer, but on Thursday denied doing so in order to lure her guests to have lunch at her home.

"I suggest that you never thought you would have to account for this lie about having cancer, because you thought that the lunch guests would die," Rogers said.

"That's not true," Patterson replied.

While being examined by her own barrister Colin Mandy, Patterson said earlier on Thursday that she did not intentionally pick death cap mushrooms, or knowingly serve them to her lunch guests.

Nor had she pretended to be sick after the lunch to avoid becoming a suspect in the case, she said.

The trial has captured public attention across Australia, where such cases are exceedingly rare.

Podcasters, journalists and documentary-makers from local and international media have descended on the town of Morwell where the trial is being held, about two hours east of Melbourne.

State broadcaster ABC's daily podcast about the proceedings is currently Australia's most popular, while many domestic newspapers have run live blogs on trial developments.

Justice Christopher Beale, the judge presiding in the case, told the jury the cross-examination of the accused would probably continue into next week.

The prosecution rested its case on Monday after a month of evidence from relatives and medical, forensic and mushroom experts.

After the defence rests, the parties will discuss whether the prosecution might seek to reopen its case in light of defense evidence, Beale told the jury.

The trial, set to conclude this month, continues.