“It’s a fairly extreme move,” said Jane Duckett, the director of the Scottish Center for China Research at the University of Glasgow. “They certainly seem to be very, very worried.”

The committee that oversees the congress said it would vote next Monday on whether to delay the gathering. Xinhua, the official Chinese news agency, quoted a committee spokesman as saying that “to ensure that attention is entirely focused on preventing and controlling the epidemic, it is considered necessary to appropriately postpone” the congress.

Yet Ms. Duckett said it would be hard for Mr. Xi to win back trust. “When you’re in charge of everything and when things go wrong, you’re responsible,” she said.

On Monday, the government sought to reassure the public that it was making progress in containing the outbreak. Officials reported that the daily count of new coronavirus cases was 2,048 — a three-week low. Over all, the virus has sickened more than 70,000 people in China and several hundred in other countries.

Public health experts said the dip in new infections was probably a result of the government’s decision to impose travel restrictions in many cities, including Wuhan, the epicenter of the outbreak.

“The measures taken have been extraordinary, and we are seeing the effects,” said Raina MacIntyre, a senior biosecurity researcher at the University of New South Wales in Australia.