The FAST party which has a majority of seats was locked out of Parliament this morning.
Today's sitting was to swear in MPs after the April 9 election.
Under the constitution Parliament must sit within 45 days of an election and today is the last day for this to be possible.
Just before midnight on Saturday, Samoa's Head of State, Tuimaleali'ifano Va'aleto'a Sualauvi II, cancelled the sitting without explanation.
The majority party in Samoa went ahead with a swearing-in ceremony today, despite being locked out of Parliament.
It was the latest twist in a constitutional crisis that has spiralled since the Head of State intervened, on Saturday, to cancel today's scheduled sitting.
The Supreme Court overturned that decision, but FAST, and its leader Fiame Naomi Mata'afa, found themselves locked out of parliament this morning.
FAST went ahead with the ceremony on the lawn outside of Parliament anyway, but no members of the Human Rights Protection Party were there.
FAST described the caretaker government's actions in locking it out of parliament as tantamount to a coup, while the leader of the caretaker HRPP party, Tuilaepa Sailele Malielegaoi, said FAST was leading a coup and would tomorrow take action.
"This is treason, and the highest form of illegal conduct," Tuilaepa said.
Earlier today
Police have surrounded Parliament in Samoa after conflicting rulings on when it can reconvene.
The Samoa Observer reports the Faatuatua ile Atua Samoa ua Tasi (FAST) party and its supporters have converged on Parliament House, calling on police to uphold the law.
Police continue to surround it and the local area. The officers were unarmed and wearing green shirts, RNZ Pacific's correspondent said.
The tense meeting follows the Speaker of Parliament's decision to disregard a Supreme Court ruling, which had cleared the way for the Legislative Assembly to convene.
The court last night had declared the Head of State, Tuimaleali'ifano Va'aleto'a Sualauvi II, acted unlawfully on Saturday in suspending Parliament.
However, the Speaker, Leaupepe Toleafoa Fa'afisi, then announced the House would not convene until a new proclamation had been made by the Head of State allowing it.
The doors to Parliament were locked, with the clerk of the house and Speaker insisting there is no sitting today - a decision that directly contravenes the court order.
Deputy FAST leader Laauli Leautea Schmidt reportedly confronted the island nation's Assistant Police Commissioner, asking why the doors were closed.
In response, Assistant Police Commissioner Auapaau Logoitino Auapaau said police were not taking sides.
The Samoa Observer reported he added that perhaps FAST and its supporters should wait for the Legislative Assembly opening ceremony to attend the building.
The extraordinary session of the Supreme Court found in favour of newcomer FAST party's challenge to Tuimaleali'ifano's edict.
FAST was expected to declare its majority when Parliament met, and announce Samoa's first woman prime minister Fiame Naomi Mata'afa.
Leaupepe, a member of the caretaker Human Rights Protection Party (HRPP) government, invoked Section 30 of the Legislative Assembly Powers and Privileges Ordinance 1960 to continue as Speaker.
"Further notice will be announced by the Office of the Clerk to officially inform Hon Members of the Legislative Assembly as well as invited guests for the State Opening of the XVII Parliament," he said.
The conflicting rulings of the Supreme Court and the Head of State set a quandary for the country, as to which has constitutional primacy.
Last night's Supreme Court challenge was heard in-chambers in front of Chief Justice Satiu Simative Perese, Justice Vui Clarence Nelson and Tafaoimalo Leilani Tuala-Warren.
Samoa's political turmoil: Conflicting rulings
Parliament was due to sit today for the swearing-in of MPs after the April 9 election. The sitting was ordered by the Supreme Court last week, after it overruled the Head of State's decision to call a second election, in order to break a deadlock that resulted from the election.
A later Supreme Court decision handed the FAST party a 26-25 seat majority, opening the way for Fiame Naomi Mata'afa to become Samoa's first woman prime minister.
Just before midnight on Saturday, local time, the Head of State, Tuimaleali'ifano Va'aleto'a Sualauvi II, cancelled today's sitting of parliament without explanation. He is understood to now be in his home village of Matautu-Falelatai, while a constitutional and political crisis has come to a head in Apia.
In an extraordinary hearing on Sunday the Supreme Court again overruled the head of state's decision, calling for Parliament to sit today. Under the constitution, Parliament must sit within 45 days of an election. Today is the last day for this to be possible.
On Sunday night, the speaker of the legislative assembly, Leaupepe Taimaaiono Toleafoa Faafisi, a member of the caretaker Human Rights Protection Party, said he would abide by the Head of State's call, not the Supreme Court ruling.