WASHINGTON (BLOOMBERG) - US President Donald Trump didn't appear at a White House briefing on the coronavirus outbreak on Tuesday (March 10), after promising a day earlier he'd hold a news conference to announce a "major" economic stimulus package.

After deciding to pursue an economic stimulus plan following the steepest drop by the benchmark S&P 500 index since 2011, Mr Trump told reporters at a briefing on Monday: "I will be here tomorrow afternoon to let you know about some of the economic steps we're taking, which will be major," he said.

But that didn't happen. The president made brief remarks and took a handful of questions after meeting with Republican senators at the Capitol earlier in the day but did not detail a stimulus plan.

"You'll be hearing about it soon," Mr Trump said at the Capitol.

He told senators that he'd like a payroll tax holiday until after the November election, according to three people familiar with his closed-door remarks.

The coronavirus briefing was the last event on the White House's public schedule for Tuesday.

During the briefing, Mr Trump's top economic adviser, Larry Kudlow, said that Mr Trump would like a payroll tax holiday to extend to the end of the year. But he declined to answer questions about how much the plan would cost or how it would work.

"Let us put the proposal out in concrete details and flesh that out and we'll have much better answers," Mr Kudlow said.

Investors have been eager for the US government to match the Federal Reserve's emergency interest rate cut a week ago with fiscal stimulus, as markets have stumbled over signs that consumer fears around the virus will cause a recession. Stocks rallied on Tuesday as the president and members of Congress batted around plans for a stimulus.

But Mr Trump's no-show at the White House briefing may raise new concerns. US stock futures opened lower on Tuesday evening as investors grew concerned economic stimulus from the Trump administration was not imminent.

Contracts on the S&P 500 fell 0.5 per cent to 2,851 as of 6.06pm in New York. The underlying gauge jumped 4.9 per cent Tuesday, capping a volatile day with a late-session rally on the expectation that the White House would deliver measures such as payroll-tax cuts and assistance to industries slowed by the spreading coronavirus.

Vice-President Mike Pence briefly addressed the economic plan in opening remarks at the Tuesday briefing.

"He's calling for payroll tax relief," Mr Pence said of the president's plan. "We're going to be working with Democratic and Republican leadership to move an economic package."

Mr Trump's promise on Monday to reveal a plan the next day dismayed some White House aides, who were still working on details of the proposal.

His proposal to waive payroll taxes might not get very far on Capitol Hill, where House Democrats and some Senate Republicans expressed reservations.