American forces conducted a drill with the South Korean navy in the Yellow Sea as well.
The Office of Joint Chiefs of Staff in Seoul said it is monitoring the situation in North Korea and "firmly maintaining readiness".
Republican Sen. Lindsey Graham voiced confidence that Trump won't allow North Korea to reach that point.
Analysts warned against reading too much into the exercises with conventional weaponry, noting that North Korea's annual winter training cycle culminates in big exercises every year around this time. It was part of celebrations marking the 85th anniversary of the founding of the country's military.
"What is different about how China is viewing the problem in North Korea today is that China is viewing that problem as a threat not only to USA interests and security, or South Korea and/or Japanese interests and security, but also a threat to Chinese interests and security.And so I think that is a big shift in and of itself", the official said.
China says the deployment of Thaad will destabilise security and there have been protests in South Korea itself, where three people were injured in clashes with police as the system was being delivered to a former golf course on Wednesday.
A rapid tempo of North Korean weapons testing in the past year has pushed Kim Jong Un's authoritarian nation closer to developing a nuclear-tipped missile that could reach the USA mainland. "The nuclear weapon would be put on an intercontinental ballistic missile that could strike the United States".
"The deployment of THAAD in South Korea would harm the efforts and the strategic balance of the region".
"So it is a sign that if the North is provoked or there is preemptive action, then a lot of Seoul and its suburbs would be within artillery range of the North".
Meanwhile, the prospect of nuclear war with North Korea increases by the hour as Trump continues to provoke the country through tough talk and empty military maneuvers in the region.
A senior Republican senator says he emerged from a dinner meeting with Donald Trump confident the president will not allow North Korea to build a nuclear-tipped missile capable of striking the United States.
In the call with Mr Xi, "the two leaders reaffirmed the urgency of the threat posed by North Korea's missile and nuclear programmes, and committed to strengthen coordination in achieving the denuclearisation of the Korean Peninsula", a White House statement said.
"The positioning of some equipment means that South Korea and the U.S. have the capability to cope with North Korea's provocations", he said.