US STOCKS-Wall St returns to losses as Buffett dumps airlines, China tensions flare

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* Pompeo says "significant evidence" virus emerged from lab
* Airlines fall as Buffet dumps stakes; Boeing also down
* Tyson drops after sales warning
* Futures fall: Dow 0.95%, S&P 500 0.66%, Nasdaq 0.60%

(Adds comments, details, updates price action)
By Shreyashi Sanyal and Medha Singh
May 4 (Reuters) - U.S. stocks were set to fall on Monday as
a U.S.-Chinese spat about the origins of the coronavirus
outbreak worsened while billionaire Warren Buffett's admission
he had dumped his airline shares crushed major U.S. carriers.
Delta Air Lines DAL.N , American Airlines Co AAL.O ,
Southwest Airlines Co LUV.N and United Airlines UAL.O fell
between 9% and 11% in premarket, after Berkshire Hathaway
BRKa.N chief Buffett told reporters of the move over the
weekend, saying "the world has changed" for the industry.
The comments, and fall in airline operators, also shaved
more than 4.7% off planemaker Boeing Co's BA.N shares.
Berkshire itself posted a record loss of nearly $50 billion
and Randy Frederick, vice president of trading and derivatives
for Charles Schwab in Austin, said Buffett's relatively bleak
reading of the market had hit home with investors.
"I did not get the sense that he sees an enormous amount of
opportunity out there right now, but is instead holding up a
very high level of cash," he said.
On China, U.S. Secretary of State Mike Pompeo said there was
"a significant amount of evidence" that the coronavirus emerged
from a Chinese laboratory. An editorial in China's Global Times
said Pompeo was "bluffing". The statements follow a grim start to May for Wall Street
last week as President Donald Trump revived the threat of new
tariffs against China in response to the COVID-19 pandemic.
"When you think how nervous markets got about the U.S.-China
trade war then if this theme continues you can't help thinking
that the end game is far worse than it would be from a simple
trade war," said Jim Reid, a strategist at Deutsche Bank.
The S&P 500 index's .SPX 29% recovery from its March lows
stands to be tested as investors weigh renewed U.S.-China
tensions and the economic damage of the health crisis.
At 8:51 a.m. ET, Dow e-minis 1YMcv1 were down 225 points,
or 0.95%, S&P 500 e-minis EScv1 were down 18.5 points, or
0.66% and Nasdaq 100 e-minis NQcv1 were down 52.5 points, or
0.60%.
Investors are also awaiting factory orders data for March,
which is expected to show a sharp decline.
With more than half of the S&P 500 companies having reported
earnings so far, analysts now see first-quarter S&P 500 earnings
falling 12.7% from a year ago, and an even sharper 37.8% decline
for the second quarter.
Tyson Foods Inc TSN.N tumbled 7.3% as the company said it
would temporarily close plants as needed and expects meat sales
to fall in the second half of this year as shutdowns hammer
restaurants and other food outlets.