Sprawling fraud factories have ballooned in war-torn Myanmar's border regions, housing scammers targeting internet users with romance and business cons worth tens of billions of dollars annually.

Myanmar's junta has long been accused of turning a blind eye but has trumpeted a crackdown since February after being lobbied by key military backer China, experts say.

Additional raids beginning last month were part of a propaganda effort, according to some monitors, choreographed to vent pressure from Beijing without too badly denting profits that enrich the junta's militia allies.

Myanmar's military descended on gambling and fraud hub Shwe Kokko on Tuesday morning, according to state media The Global New Light of Myanmar.

"During the operation, 346 foreign nationals currently under scrutiny were arrested," it said.

"Nearly ten thousand mobile phones used in online gambling operations were also seized."

Since a 2021 coup sparked a civil war, Myanmar's loosely governed borderlands have proven fertile ground for scam hubs which analysts say are staffed by thousands of willing workers as well as people trafficked from abroad.

But the junta's military backer China has been increasingly irked at the number of its citizens who are both perpetrators and victims of the scams, experts say.

The junta on Wednesday blamed armed opposition groups for allowing scam centres to operate under their protection, but said it had taken action after wrestling back territorial control.

The Global New Light of Myanmar said the Yatai firm of Chinese-Cambodian alleged racketeer She Zhijiang was "the entity involved" in running the Shwe Kokko area.

She was arrested in Thailand in 2022 and extradited last week to China where he faces allegations of involvement in online gambling and fraud operations.

She and his company Yatai were previously under British and US sanctions.

Washington says he transformed a village on the Myanmar-Thai border into Shwe Kokko -- "a resort city custom built for gambling, drug trafficking, prostitution, and scams targeting people around the world".

In October, Myanmar's junta announced raids on nearby scam centre KK Park, where it says it is currently demolishing more than 600 buildings.

A highly publicised sweep starting in February saw around 7,000 alleged scammers repatriated and Thailand enact a cross-border internet blockade.

Scam victims in Southeast and East Asia alone were conned out of up to $37 billion in 2023, according to a UN report, which said global losses were likely "much larger".