At least 53 people have died in an ambush in Papua New Guinea's remote Highlands region.

The victims were shot dead during a tribal dispute in the Enga Province over the weekend, a national police spokesman told the BBC.

Authorities have appealed for calm, and say they expect the death toll to climb.

The Highlands area has long struggled with violence, but these killings are believed to be the worst in years.

Police have started collecting bodies at the scene near the town of Wabag - roughly 600km (373 miles) northwest of the capital Port Moresby.

"This is by far the largest [killing] I've seen in Enga, maybe in all of Highlands as well," Royal Papua New Guinea Constabulary Acting Supt George Kakas said, according to the Australian Broadcasting Corporation (ABC).

"We're all devastated, we're all mentally stressed out. It's really hard to comprehend."

Escalating tribal conflict - often over the distribution of land and wealth - led to a three-month lockdown in Enga Province last July, during which police imposed a curfew and travel restrictions.

In recent years, an influx of illegal firearms has made clashes more deadly and fuelled the cycle of violence.

Governor Peter Ipatas said that there had been signs that fighting was about to erupt again ahead of the ambush, according to the ABC.

"From a provincial perspective, we knew this fight was going to be on and we [alerted] the security forces last week to make sure they took appropriate action to ensure this didn't occur."

Security more broadly remains a key concern for PNG. The government last month declared a state of emergency after major rioting and looting left at least 15 people dead.

Australia - one of the country's closest allies - said news of the killings was "very disturbing".

"We're providing considerable support, particularly for training police officers and for security in Papua New Guinea," Prime