Taiwan thanked the United States on Thursday for agreeing to sell 40 howitzer artillery systems in a $750 million deal that will help the island better defend itself from a Chinese invasion.

Taipei's foreign ministry said Thursday it was the first major arms sale announced since President Joe Biden took office in January and would help the island "maintain a rock-solid self-defence and regional peace and stability".

"Faced with China's continuing military expansion and provocations, our government will boost national defence and security with an unwavering determination to defend people's lives and our free and democratic way of living," it added.

The State Department approved the sale of 40 155mm M109A6 medium self-propelled howitzer artillery systems on Wednesday in a deal that will need to be approved by Congress.

Taipei's foreign ministry said it was the first major arms sale announced since President Joe Biden took office in January and would help the island "maintain a rock-solid self-defence and regional peace and stability".

"Faced with China's continuing military expansion and provocations, our government will boost national defence and security with an unwavering determination to defend people's lives and our free and democratic way of living," it added.

The State Department approved the sale of 40 155mm M109A6 medium self-propelled howitzer artillery systems on Wednesday in a deal that will need to be approved by Congress.

Democratic and self-ruled Taiwan lives under constant threat of invasion by authoritarian China, whose leaders view the island as part of their territory.

They have vowed to one day seize Taiwan, by force if necessary.

Under President Xi Jinping, Beijing has ramped up military pressure.

Chinese fighters and bombers now probe the island's air defence zone on a near-daily basis, sand dredgers have increased activity around islands close to the mainland and the People's Liberation Army has publicised a host of drills simulating a Taiwanese invasion.

Washington diplomatically recognises Beijing over Taipei but it is also bound by an act of Congress to sell Taiwan weapons to defend itself.

In contrast to treaty allies such as Japan, South Korea and the Philippines, the United States has never openly committed to defending Taiwan if it was invaded -- a policy known as "strategic ambiguity".

But it maintains that any change to Taiwan's future status must not be done by force.

Taiwan's military is dwarfed by China's, and much of its equipment, including its fleet of fighter jets, is ageing.

Moveable howitzers would be key to halting an invasion, enabling Taiwan's military to direct fire at incoming troop transport ships and shell landing beaches.

Former US president Donald Trump ramped up big-ticket arms sales to Taiwan during his time in office as he feuded with Beijing on a host of issues from trade to national security.

Sales included drones, missile systems and new-generation fighter jets.

Biden has been more open to working with China on common causes such as climate change.

But he has maintained much of Trump's more robust policies when it comes to China's human rights abuses in places like Hong Kong and Xinjiang as well as its threats against Taiwan.

Defending Taiwan from any Chinese invasion has also become a rare bipartisan issue in Washington and Congress approval of the howtizer sale is likely.