Samoa election: Prime Minister Tuilaepa Sailele Malielegaoi appeals court ruling that'd make rival Fiame Mata'afa country's first-ever female leader

There's been a significant and historic breakthrough in Samoa's deadlocked election - but a historic court decision that paves the way for a change in leadership has been appealed just hours after it was handed down.

Two Supreme Court decisions have ruled in favour of the newcomer FAST Party, meaning the country could be on the verge of installing its first-ever female Prime Minister. 

There were celebrations and songs outside Samoa's Supreme Court on Monday. The road to victory for the ruling HRPP and the opposition FAST party has been dogged with uncertainty and controversy.

But opposition leader Fiame Mata'afa now looks set to be the country's newest leader.

"Obviously we've seen some decisions made today where this could be the final outcome. It feels significant to me," New Zealand Prime Minister Jacinda Ardern said.

Until Monday it had been evenly split, with both parties on 26 seats. 

"That, as of today's court decision, seems to be no longer. So essentially we are back to our April 9 elections - 26 FAST and 25 HRPP," said Samoa Global News editor Tuiloma Sina Retzlaff.

The court threw out a move by the Electoral Commission to appoint an extra female MP, which created the deadlock. It also overruled a move by the Head of State for new elections to be held this Friday. 

"That decision or writ by the Head of State has also been declared by the Supreme Court as unlawful," Retzlaff said.

Tuilaepa Sailele Malielegaoi has been Prime Minister for 23 years. Fiame Mata'afa was Tuilaepa's former deputy, but defected over controversial land rights legislation.

Her party now has the majority. 

But like everything so far in this historic and somewhat turbulent election, nothing comes easily. It's understood Tuilaepa has now launched an appeal over Monday's court rulings.