Frederick Kologeto, leader of the People First Party, was among 10 ministers to confirm their resignations on Monday.
The departure of the 10 men means Mr Manele is without more than half of his cabinet, and unlikely to command the support of a majority of parliament needed to continue governing.
Mr Kologeto's PFP has opted to join the opposition, which could table a motion of no confidence.
"There are issues between us and the coalition partners, and we don't see any resolution to this, so we decided to move," he told Radio NZ.
"There were a few issues between us, I think one is trust."
Mr Manele has asked citizens for calm as he navigates his government's collapse.
"For now, the priority is for the public service to continue its important work while political leaders engage to resolve the issues before us," he said in a statement.
"It is too early to speculate on any outcome, and we will continue to keep the public informed as developments unfold."
Both the Solomon Islands and Mr Manele are not strangers to political manoeuvres such as this, with cabinet posts and even the prime ministership changing hands in between elections.
Since taking office in 2024, Mr Manele has stared down two no-confidence pushes, both championed by former leader Gordon Darcy Lilo.
After the resignation of cabinet ministers in April 2025, Mr Manele defeated a no-confidence vote by appointing new ministers from opposition and rejuvenating his coalition.Â
Local outlet Island Sun reported Mr Lilo was spotted dining at a Chinese restaurant with senior PFP MPs on Sunday.
Should a fresh no-confidence vote be tabled from this week's departures, it would not be debated in parliament until next week at the earliest.
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