Workers disinfect closed shop lots following the coronavirus outbreak in Hubei, China, on Monday. Officials reported the highest single-day death toll since the epidemic began.

Cheng Min/AP

Updated at 10:40 a.m. ET

The head of the World Health Organization is warning that a few cases of the novel coronavirus that have been spread by people who never traveled to China could be “the tip of the iceberg,” as officials reported the highest single-day death toll since the epidemic began.

Meanwhile, Chinese authorities lashed out at Western media reports that Beijing was not fully cooperating with international health experts.

In a tweet on Sunday from Geneva, WHO Director-General Tedros Adhanom Ghebreyesus said the “spread outside #China appears to be slow, but could accelerate.”

“The detection of a small number of cases may indicate more widespread transmission in other countries; in short, we may…