NZ Prime Minister

'Kia ora Jacinda!' - Rihanna hits up the Prime Minister on Twitter

"Kia ora @jacindaardern!," she wrote.

"It's been a big year for you & [New Zealand] - congrats!"

The 'Diamonds' singer told Ardern her year could "get even better" if she pledged funds to the Global Partnership for Education.

"I hope you & @MFATgovtNZ agree that educating every child can change the world!" she added.

The organisation is working alongside Rihanna's own charity, the Clara Lionel foundation, to provide education for children in poor countries around the world.

Twitter reacts to Ardern baby news: 'Such a great role model'

Ms Ardern, who became Prime Minister in October, announced this morning, via Instagram, that she and partner Clarke Gayford were expecting a baby in June.

Former Prime Minister Helen Clark was among the first of many to congratulate Jacinda Ardern on her pregnancy.

Ms Clark said via a tweet it was going to be a "super busy year" with "much to look forward to".

"Every #woman should have the choice of combining family & career."