Eight Tongan business operators, whose properties were gutted by fire during riots in Nuku'alofa six years ago, are suing the insurance company, National Pacific Insurance.
Matangi Tonga reports the company has refused to pay out because it believes the destruction during the riots was planned.
Among those called as witnesses has been the leader of the opposition Democratic Party, Akilisi Pohiva, who has previously been charged with sedition in connection to the riot.
He was acquitted, along with several others in 2009, and Radio Tonga reports he told the court this week that when his pro-democracy supporters threw rocks he shouted for them to stop.
Mr Pohiva says while they wanted political change, they wanted it implemented in a legal and peaceful way.
Up to 40 witnesses are expected to be called by both parties during the trial in which millions in damage is believed to being claimed.