TOKYO (AFP) - In scenes reminiscent of films like "Transformers", a giant US robot fighting machine swung a "chainsaw sword" to chop a Japanese opponent into submission in a battle watched by tens of thousands online.

The two massive and heavily armed machines went claw-to-claw at an abandoned steel mill in Japan, firing cannons and smashing each other in a days-long duel.

California-based firm MegaBots wheeled out its Eagle Prime fighting machine - weighing in at 12 tons and with 430 horsepower behind it.

Pitted against Eagle Prime was KURATAS, a lighter (6.5 tonnes) and less powerful (87 horsepower) robot created by Japanese company Suidobashi Heavy Industry.

KURATAS had won a preliminary bout against American opposition, pounding its counterpart with an iron fist.

But its bludgeoning appeared to inflict little damage on Eagle Prime, which fired cannons from its arm in a bid to destroy the Japanese machine's sensitive electronics.

During the bout, Eagle Prime swapped its cannon arm for its four-foot chainsaw, capable of severing rocks, which swung the battle in its favour.

It sliced off KURATAS' fingers before savaging its right arm and pushing its Japanese opponent against metal frames left inside the steel mill.

The severe damage forced Suidobashi Heavy Industry's founder and pilot Kogoro Kurata to surrender.

"I think it's time to make this a sports league," declared MegaBots co-founder and pilot Gui Cavalcanti.

"I think it's time to get rules, weight classes and bring this show on the road," he said.

The video of the show was shot over multiple days with no live audience for safety reasons to ensure the machines could unveil their full destructive power, MegaBots said in a statement.

The live-stream of the video was watched by more than 186,000 people on Oct 17, before being distributed to a wider audience via YouTube and Facebook.