California makes third gender official

California's Senate Bill No 179 comes into effect in 2019. Photo / Getty Images

California has become the first US state to officially recognise a third gender.

People in the state can now identify as male, female, or nonbinary on any legal documents, including driver's licences and birth certificates.

The bill, signed by Governor Jerry Brown on Sunday, will go into effect in 2019.

It will also remove the need for a doctor's statement for any gender changes in official documents.

Gov signed our SB179: allows ppl to identify as non-binary, easily correct gender. Big win 4 notion ppl should be allowed to be who they are

— Senator Scott Wiener (@Scott_Wiener) October 16, 2017

"I want to thank Gov Brown for recognising how difficult it can be for our transgender, nonbinary, and intersex family members, friends, and neighbours when they don't have an ID that matches their gender presentation," Senator Toni Atkins, the bill's co-author, told Buzzfeed.

Activists are calling the bill "an important moment in history".

"We as a society need to learn that biological sex and gender identification, which are very different from each other, occur along a spectrum," activist Sara Kelly Keenan told Buzzfeed.