A 7-year-old boy has been accidentally shot and killed by his younger brother in Tonga after the pair found a loaded gun in the family car.

Tonga Police said emergency services responded to reports of a shooting at a property in the village of Ha'ateiho, on the main island of Tongatapu, on Friday evening.

A police statement released last night said the 7-year-old and his 4-year-old brother had been inside the vehicle when they found a .22 hunting rifle.

"When the 4-year-old got hold of the gun, he fired four shots at his 7-year-old brother, which tragically caused his death," Tonga Police said.

Local authorities have since arrested their 40-year-old father for possession of unlicensed ammunition and other firearm-related charges.

Chief Superintendent Filipe Fifita called on local gun owners to be responsible about the way their firearms and ammunition were stored.

Second accidental shooting death involving children

"We are reminding firearms licence holders to take their responsibility with safe storage of their firearms seriously."

Fifita acknowledged this was the second accidental shooting death involving young people in just over a year, after a similar incident in which an 18-year-old was killed last year.

In that incident, a 12-year-old boy was charged with manslaughter by negligence over the death in Kolomotu'a in Nuku'alofa, the Tongan capital city.

"It was only in April last year that an 18-year-old male died from an accidental shooting and now we have lost another young life in a similar situation that could have been avoided," Fifita said.

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Police in the island nation are now calling on members of the public to notify authorities or surrender any unlicensed firearms in their possession.