China has already suspended planned exchange of military visits with the US and is also threatening to impose sanctions on any US companies involved in the deal.
"The Taiwan issue involves China's sovereignty and integrity, which concerns China's core interests," a Chinese defence ministry spokesman said on Saturday.
"China is resolved not to yield or compromise on this issue. China's army will be determined in fighting against any conduct that threatens China's sovereignty, integrity and national security."
He Yafei, the Chinese vice-foreign minister, earlier told Jon Huntsman, the US ambassador to China, that the arms deal could jeopardise bonds with Washington.
But Laura Tischler, a US state department spokesman, justified the arms sale, saying: "This is a clear demonstration of the commitment that this administration has to provide Taiwan the defensive weapons it needs and as provided for in the Taiwan Relations Act."
She said that the deal would contribute to "maintaining security and stability across the Taiwan Strait".
|Al Jazeera speaks to Yue Xiaoyong, China's ambassador to Qatar, about the US decision
Taiwan welcomed the US decision, with Ma Ying-jeou, the country's president, saying the deal would help the island further develop ties with China.
"It will let Taiwan feel more confident and secure so we can have more interactions with China," he was quoted by Taiwan's Central News Agency as saying.
The developments incidentally come against a backdrop of steadily improving relations between the two countries.
Speaking to Al Jazeera on Saturday, Christian Ford, Beijing bureau chief for the US newspaper Christian Science Monitor, said that while tensions between China and the US have been rising, those between China and Taiwan have been abating in recent months.
"The two sides have been discussing trade and investment issues ... there are now many more flights from Beijing to Taiwan," he said.
"The actual situation in the streets is not tense. In fact, it's a great deal less tense than a couple of years ago. But when you look at relations between and Washington and Beijing, there are definitely some more hiccups on the horizon."
Beijing regards Taiwan as a renegade province and has vowed to bring the island eventually back under mainland rule, by force if necessary.
The US government, on the other hand, is bound by the 1979 Taiwan Relations Act, which obliges Washington to ensure the island is capable of responding to Chinese threats, and to sell defensive weapons to it.
|The US announced it was selling $6.4bn worth of military hardware to Taiwan [Reuters]
The Obama administration told the US congress on Friday of the proposed sales, which include Black Hawk helicopters, Patriot "Advanced Capability-3" anti-missile missiles and two refurbished Osprey-class mine-hunting ships.
Philip Crowley, a state department spokesman, said that the arms sales were consistent with the three key communiques between the United States and China when they normalised relations.
However, Yue Xiaoyong, China's ambassador to Qatar, told Al Jazeera that the arms sales were "a clear violation of the three joint communiques".
"It's a clear violation of China's sovereignty and territorial integrity," he said.
In 2008, China suspended most military dialogue with Washington after the administration of George Bush, the former president, approved a $6.5bn arms package to Taiwan that included guided missiles and attack helicopters.