A Police Inspector and two constables will be charged with manslaughter along with two other police constables in relation to the death of the New Zealand police officer Kali Fungavaka, Tonga's Police Commissioner said today.

The senior officer was arrested today and will appear in the Nuku'alofa Magistrate's Court this afternoon to be charged with manslaughter. He was a supervising officer working on the night in which New Zealand Police Officer Kali Fungavaka was fatally injured while in police custody.

Police Commissioner Grant O'Fee revealed the new development in the homicide investigation and said that the senior commissioned officer in the rank of inspector, and two constables were all working on duty on the night of August 17. The three would appear in open court at the Nuku'alofa Magistrate's Court at 2pm today, September 27.

Commissioner O'Fee said there were now five police officers to be charged with manslaughter.

The two constables who were first charged with common assault, Salesi Maile and Fatai Faletau, would have their charges formally upgraded to manslaughter when they appear at the Magistrate's Court on Monday, October 1. At the same time the other three newly charged police would also appear in the lower court again.

Meanwhile, the detainee Semisi Kalisitiane Manu remained charged with manslaughter and was held in police custody,  and also would appear in the lower court on October 1.

He said the new arrests were the result of more people, both inside the police and outside police, who had came forward.

"We interviewed them and all evidence was evaluated by us and the Solicitor General's Office and it was determined this was the appropriate charge to be made," he said.

The five police officers were currently suspended from the Tonga Police as the investigation continued, he said.

The Australian Federal Police investigator was expected to arrive in Tonga on October 18.

"I am grateful to Deputy Commissioner 'Unga Fa'aoa and his team for their good work and I am confident the investigation was done with integrity," he said.