The World Health Organization said Thursday it was too early to declare a peak in the spread of the coronavirus, a day after China marked its deadliest day since the outbreak began.

Separately, Singapore—home to the second-largest number of cases outside mainland China—reported two new infections, including one with no apparent link to China. The city-state warned the public to be “prepared for the possibility of new infection clusters involving locals within the community,” and that future cases might not arise from recent...