Ghebreyesus was speaking after WHO's emergency committee met for a second day on Thursday to debate the epidemic but were divided over whether or not to declare it an emergency.
Prof Didier Houssin, the chair of the emergency committee, said it was "too early" to consider it a "public health emergency of international concern" which would have designated the epidemic a serious global public health event.
The international organisation said they could reconvene the committee if the situation changes.
Travel lockdown in China
The announcement comes after China locked down three cities and their 18 million residents in an unprecedented effort to try to contain the deadly new coronavirus that has spread in the Lunar New Year travel rush.
Outbound flights were cancelled and normally bustling streets, shops, restaurants and other public spaces in the city were eerily empty.
Police, SWAT teams and paramilitary troops guarded the city's train station, where metal barriers blocked the entrances.
“To my knowledge, trying to contain a city of 11 million people is new to science," Gauden Galea, the World Health Organization's representative in China, told the AP, speaking about Wuhan, a city at the epicentre of the crisis.
“It has not been tried before as a public health measure. We cannot at this stage say it will or it will not work."
Similar travel restrictions will apply in nearby cities Huanggang and Ezhou from Friday.
At least 600 people have been diagnosed with the virus and 17 people have died, French health minister Agnès Buzyn said on Thursday, citing Chinese authorities. Chinese authorities announced an 18th fatality, the first outside of Hubei province, on Thursday, according to AFP.
Outside of China, there have been cases in the United States, Japan, Thailand, and South Korea.
Ghebreyesus said that the measure in Wuhan was "strong" but that China would "minimise the chances of this outbreak spreading internationally".
"We commend their actions," he added, stating that the WHO will get more information from their team on the ground.