The trouble apparently began with the discovery of decapitated Simon Gawi's body, a teacher from Pangia in the Southern Highlands. Gawi was employed as a teacher at Bau Primary School in Madang's Four Mile area.
This discovery started the violence which resulted in the loss of three more lives, injuries and vandalism of the city's water plant, making it inoperable.
Madang's water treatment plant was subject to extreme vandalism. The Madang Chamber of Commerce and Industry reported that the vandalism included severe damage to the switching box, cut wiring to water pumps and a generator was partially damaged by fire.
There was also damage to the water plant's buildings caused by felled tree and power lines brought down, also by felled trees. Water mains were cut and pipes were destroyed, leaving residents and businesses without water.
Early estimates predict it will cost about K2 million to repair the water plant.
The head of the deceased teacher was only discovered later in the week and given to the Madang Province Governor's office on Thursday night.
Guard Dog Security Services reported that the presence of the reinforcement of police personnel from Lae and Goroka had helped in the calming of the situation.
"Businesses, offices and other services in Madang town continue to operate as normal. Police forces are closely monitoring the situation to prevent further violence and crimes," Guard Dog said.
The security firm noted that the water supply had been restored, with pumps operational from Thursday night.
Earlier, it was reported that Madang MP Bryan Kramer met with the rioters, who apparently told him that they were "simply peace-loving locals who were showing strength against the opportunists and other ethnic groups who they claimed to be entering the province and destroying their peaceful way of life".