Wall Street got a boost this week from optimism around a potential coronavirus vaccine and the US reopening its economy.
The S&P 500 gave up 0.8%, but is on track to close out the week with a weekly gain.
Investors have also greeted gradual steps by states to reopen their economies.
President Donald Trump's warning on Thursday that the USA would react strongly to China's plan for a national security law in Hong Kong has raised concerns over Washington and Beijing's possibly reneging on their Phase 1 trade deal.
Stocks closed broadly lower on Wall Street Thursday as investors weighed more data showing the economic damage being caused by the coronavirus pandemic and another flareup in tensions between the US and China. USA stocks finished higher on Wednesday as market fears were partly relieved after President Donald Trump's comments on Iran's missile strike against Iraqi bases housing US forces.
The S&P 500 posted six new 52-week highs and no new lows; the Nasdaq Composite recorded 62 new highs and nine new lows.
The Dow Jones Industrial Average fell 101.78 points, or 0.4%, to 24,474.12.
Later, major indexes were led higher by gains of popular tech stocks including Facebook and Apple.
The S&P 500 rose 6.94 points to 2,955.45.
Trump's risky new re-election strategy: Waging war with Obama
Last week Trump urged Senator Lindsey Graham, who chairs the powerful Senate judiciary committee, to call Obama to testify. Without presenting any evidence, Trump claimed in a Fox Business News interview, "this was all Obama, this was all Biden".
Whether it is an ember or a flame, we are going to put it out. The Nasdaq composite was up 0.4%.
The Nasdaq index is down about 5% from its February 19 record high, helped in recent weeks by gains in Microsoft, Amazon and other heavyweight companies seen coming out of the economic downturn stronger than their smaller rivals. The heavyweight financial and energy sectors were the largest percentage decliners.
Oil prices fell, snapping a six-day winning streak. The global benchmark, Brent crude futures, were down $1.67, or 4.63% to $34.39 a barrel.
Crude oil started the year at about $60 a barrel, but plummeted earlier this year as demand sank due to widespread travel and business shutdowns related to the coronavirus. China's government pulled its annual target for economic growth for the first time in decades because of uncertainty from the coronavirus pandemic.
"I still think this is going to be a hard period for oil because even if the economy is reopened, it doesn't mean that behaviourally people are just going to go back to the way things were".
Bonds yields were mixed. European markets shook off some early weakness and were mostly mixed.
On the other hand, China released draft legislation that is seen as Beijing's attempt to ramp up its control over Hong Kong.
The proposed bill is aimed at forbidding secessionist and subversive activity, as well as foreign interference and terrorism.
"The United States strongly urges Beijing to reconsider its disastrous proposal, abide by its global obligations, and respect Hong Kong's high degree of autonomy, democratic institutions, and civil liberties", U.S. Secretary of State Mike Pompeo said on Friday.