As the world anxiously waits for North Korea's next nuclear provocation, the billion-dollar weapons industry is already cashing in.

With each missile test and nuclear explosion underneath Kim Jong-un's H-bomb mountain, South Korea and the US are deploying their own show of force.

US President Donald Trump took to Twitter this week to reveal Japan and South Korea were buying up an enormous amount of military hardware from their American ally.

Trump’s tweet followed a Monday call with the South Korean President Moon Jae-in, during which he provided his "conceptual approval for the purchase of many billions of dollars' worth of military weapons and equipment from the United States by South Korea".

Dr Adam Broinowski, a leading expert on North Korea, told nine.com.au the South Korean deal would be worth somewhere under the $37.5 billion (US$30 billion) mark.

"The largest weapons deal with a foreign country is to Saudi Arabia and that was around the US$100 billion ($125 billion), that's huge, that's much larger than most deals. Then the second largest is around US$30 billion," Dr Broinowski said.

"It would probably be under (US$30 billion) – those are very large sums which would be ranging across a plethora of weapon systems. It really depends in this case what they discussed."

He said the arms race has heated up dramatically and major hardware was being moved frantically through the region.

"This increased threat increases the military activity which only boosts the arms race. It is precisely what has been warned in the past and it is what is happening now," he said.

"If you don't rely on dialogue and you rely on brute force, the weapons industry capitalises on it while the threats only escalate and you don't reach any agreement or negotiation, it's a dead end."

Trump's declaration of selling more weaponry to South Korea comes as the US military attempted to install more Terminal High-Altitude Area Defence Systems (THAAD) in the region.

The installation resulted in South Korean locals clashing with police in the farming village where the weapons are being fitted. Thirty-eight people, including six police officers, were injured.

Residents of Seonju County, North Gyeongsang Province, are worried over rumoured health hazards linked to the system's radar, and the possibility the town will become a target of North Korean attacks.

Dr Borinowski said each THAAD system costs about $1.6 billion and takes about $27.5 million a year to maintain.

He said part of America’s reluctance to offer more than brute force when dealing with North Korea is linked to the economic boost the weapons industry provides the nation.

"It's not the only reason of course," he said.

"The weapons industry is certainly taking the opportunity to capitalise on this extremely tense, difficult situation by making the argument that these sorts of expensive weapons are required for self-defence."

For the fiscal year of 2016, the US State Department cleared more than $41 billion (US$33 billion) worth of foreign weapon sales, Defense News reported in December last year.

At the time, the industry publication said if the trend held up, "2017 would be on pace to beat the US$68.6 billion ($85.8 billion) record in total foreign weapons sales, set in 2012".

While Trump's tweet has suggested the approval of selling more weapons to Japan and South Korea was simple, it this may not be the case.

Professor Andrew O'Neill of Griffith Business School told nine.com.au Trump's messaging is “quite simple” in the sense that there is an assumption it’s going to happen “next week or next month or even next year”.

He said the move was more of a signal to both allies and to the likes of China and North Korea "that the US is more than happy to be injecting a lot more money into these countries military inventories".

"The reality is foreign military sales are a very formal, complicated process that the US has even with really close allies,” he said.

"What has to happen is a formal request from countries to purchase specific US equipment and then those requests have to go through the State Department and if they sign off on that it then has to go to the Pentagon and it ultimately it has to be approved by Congress.