Prime Minister Scott Morrison has blasted a push to allow parents in Tasmania to choose whether to include their baby’s sex on a birth certificate.

Mr Morrison labelled the transgender rights reforms, put forward by the Labor opposition and Greens, as “ridiculous”, after they passed the Tasmanian lower house on Tuesday night.

"Labor's plan to remove gender from birth certificates in Tasmania is ridiculous," Mr Morrison tweeted on Wednesday.

"Bill Shorten should step up and commit to put motion to ALP Federal Conference to outlaw it."

Transforming Tasmania spokesperson Martine Delaney hit back at the prime minister’s comments claiming they were “ill-informed”.

Labor’s plan to remove gender from birth certificates in Tasmania is ridiculous. Bill Shorten should step up and commit to put motion to ALP Federal Conference to outlaw it. — Scott Morrison (@ScottMorrisonMP) November 20, 2018

“A heck of a lot of people have been quick to pass judgement. He [Scott Morrison] is doing so – I think - from a very ill-informed base," Ms Delaney told SBS News.

“If he took the time to actually talk to people and find out what this is about, he would find out this is not actually ridiculous, this is common sense and this is justice.

READ MORE Tasmania could become first state to remove gender from birth certificates

“There a lot of people who are very quick to pass judgement without taking the time to find out what is going on and I think that’s what has happened with Mr Morrison here.”

Ms Delaney said after years of lobbying - with dedicated activists - she was "hopeful" the reform was going to pass the upper house to create an "even playing field" for the transgender and the gender diverse community in Tasmania.

"[The reform] actually affects most Tasmanians in no measurable way, but makes an enormous difference to the lives of transgender and gender diverse people and I think upper house members understand that and I am pretty confident we will see these amendments pass," Ms Delaney told SBS News.

The changes were passed in the lower house by the casting vote of rogue Liberal Speaker Sue Hickey, who voted against her party.

The bill also allows people aged 16 or older to change the gender on their birth certificate by filling out a statutory declaration.

Liberal Attorney-General Elise Archer believes the amendments are deeply flawed.

"This amended bill contains legally untested, unconsulted and highly problematic changes that we could not support," she said in a statement.

Transforming Tasmania Media Release

Tuesday November 20th 2018

TAS GENDER ADVOCATES APPLAUD LANDMARK REFORMS AS ATTENTION TURNS TO UPPER HOUSE pic.twitter.com/kDknovmrd0 — Transforming Tasmania (@TransformingTas) November 20, 2018

"These changes will make people, who we should all care about, feel happier, safer and more included," Greens leader Cassy O'Connor told parliament.

The bill must pass Tasmania's upper house, comprising mostly independents, before becoming law.