Wall Street has snapped a four-day winning streak, with a halted COVID-19 vaccine trial and an elusive US stimulus agreement weighing on sentiment as third quarter earnings season kicks off.

All three major US stock indexes slipped into the red by mid-afternoon.

Johnson & Johnson announced on Monday it was pausing clinical trials of a COVID-19 vaccine candidate due to an unexplained illness in a study participant.

The delay weighed on the company’s shares even after its beat-and-raise earnings report.

Its shares were last off 2.5 per cent.

“It shows once again that the vaccine is still far away, and it’s a good thing that so many pharmaceutical companies are working on it,” said Oliver Pursche, president of Bronson Meadows Capital Management in Fairfield, Connecticut.

“JNJ looked promising just a few weeks ago and now here’s a complete turnaround.”

Hopes for the passage of a new coronavirus relief package faded as US House Speaker Nancy Pelosi rejected the $US1.8 trillion ($A2.5 trillion) coronavirus relief proposal from the White House, saying it “falls significantly short of what this pandemic and deep recession demand”.

Meanwhile, millions of people across the US struggle to make ends meet nearly two and a half months after emergency unemployment assistance expired.

JPMorgan Chase & Co and Citigroup Inc were the first two major US banks to report third-quarter results.

Although JPMorgan handily beat consensus profit estimates, gaining from a boom in its trading business, its peer Citigroup, while also beating expectations, was slammed by low interest rates and a slowdown in loan demand.

Their shares were down 1.7 per cent and 4.4 per cent respectively.

Apple Inc unveiled the latest incarnation of its flagship gadget, the iPhone 12 with 5G connectivity.

Its shares were down 3.3 per cent.

The Dow Jones Industrial Average fell 158.04 points, or 0.55 per cent, to 28,679.48, the S&P 500 lost 22.51 points, or 0.64 per cent, to 3,511.71 and the Nasdaq Composite dropped 12.36 points, or 0.1 per cent, to 11,863.90.

Third-quarter reporting season has left the starting gate, and analysts now expect S&P 500 earnings, in aggregate, to fall by 19.6 per cent year-on-year, according to Refinitiv.

Other earnings on tap this week include Bank of America Corp , Goldman Sachs Group Inc, Wells Fargo & Co, UnitedHealth Group and United Airlines Holdings Inc expected on Wednesday, with Morgan Stanley and Honeywell International Inc due on Thursday.

Shares of Delta Air Lines Inc dropped 2.4 per cent after the commercial carrier reported a 76 per cent plunge in quarterly revenue and announced it has delayed a targeted halt to its cash bleed.

Plane maker Boeing Co reported order cancellations for its grounded 737 MAX aircraft and said deliveries were less than half the number as the same month a year ago.

Its stock was down 2.5 per cent and was the heaviest drag on the Dow.

Declining issues outnumbered advancing ones on the NYSE by a 2.26-to-1 ratio; on Nasdaq, a 1.50-to-1 ratio favoured decliners.

The S&P 500 posted 37 new 52-week highs and one new low; the Nasdaq Composite recorded 107 new highs and 10 new lows.