JoAnn Gregoli, a 30-year veteran of wedding and event planning, has advice for couples with weddings on the horizon: don’t cancel because of the coronavirus, but instead, postpone.

“I’ve gone through the swine flu in Mexico, I’ve gone through the avian flu — this is uncharted waters,” Ms. Gregoli said.

With worldwide cases now surpassing 100,000, the New York-based planner has seen the panic begin to set in for wedding industry professionals whose businesses rely on dresses manufactured in China, or flights to destination ceremonies and honeymoons, or even organizing large groups of people.