Tonga's Prime Minister Siaosi Sovaleni resigned on Monday, his office and parliament officials said, ahead of an expected motion for a vote of no confidence. 

"I'll be resigning immediately according to the constitution," Sovaleni told the Pacific nation's parliament, according to a report on the Matangi Tonga news website citing the parliament office.

"Yes, the prime minister has resigned but we're not sure what happens next. The parliament returns this afternoon," parliament official Rhonda Hufanga told AFP.