In his tweet, Mr Trump wrote: “The coronavirus is very much under control in the USA. We are in contact with everyone and all relevant countries.
“CDC & World Health have been working hard and very smart. Stock market starting to look very good to me!”
The Dow’s drop is the third-worst in its 124-year history.
Users on Twitter were quick to debunk and attack Mr Trump’s claim, with one writing: “I believe #WallStreet is telling you you’re a despicable pathological liar and not to be trusted with Americans’ health and welfare.”
Another tweeted: "A 'very good' stock market is AFTER it goes down 1000... and you WONDER why people call you unstable?"
The president’s tweet comes as his government faces criticism for its handling of the outbreak. While the Centers for Disease Control and Prevention has developed a monitoring system for the disease, it has had problems rolling it out.
Meanwhile, deputy homeland security Ken Cuccinelli is under fire for asking the public on Twitter where to find information about the outbreak, saying he was having trouble accessing John Hopkins University’s map of the infection’s progress.
The Trump administration has now requested that Congress grant it $1.25bn in extra funds to fight the outbreak.
However, former Obama administration cabinet member Chris Lu pointed out that the administration’s budget is already planning to cut funds from agencies best placed to deal with the virus’s spread.
Lu also wrote that Trump is “more concerned about health of stock market than public health”.
Some perspective on Trump's $2.5 billion #coronavirus request:
-His budget cuts $3 billion from global health programs, $3 billion from NIH, and another 16% from CDC
-He's eliminated WH pandemic position
-He's more concerned about health of stock market than public health https://t.co/KyeJRYFzvI— Chris Lu (@ChrisLu44)February 25, 2020
Outside the US, both China and South Korea have reported more coronavirus cases, with the Chinese government now reporting 77,658 cases on the mainland and 2,663 deaths.
The number of cases is also growing in the Middle East, with Iraq and Afghanistan closing their borders with Iran and Bahrain temporarily suspending flights to and from Dubai, the world’s busiest airport.
In Italy, seven people have died from the virus, with 229 testing positive. Authorities have put up manned checkpoints around a dozen quarantined northern towns, and Austria has temporarily halted rail traffic across the Italian border.
A World Health Organisation advisor has warned that the disease is “rapidly becoming” the the organisation’s category of a “disease X” – a new pathogen not known to the organisation that may potentially cause a pandemic.