Hospitals in China appear to be filling up amid concerns about a fresh Covid-19 wave hitting the country, the World Health Organization (WHO) says.
Dr Michael Ryan says intensive care units (ICU) are busy despite officials saying numbers are "relatively low".
China figures show no-one died of Covid on Wednesday but there is scepticism about the disease's real impact.
In recent days hospitals in Beijing and other cities have been filling up as the latest Covid surge hits China.
Since 2020, China has imposed strict health restrictions as part of its zero Covid policy.
But, the government ended most of those measures two weeks ago after landmark protests against the strict controls.
The number of cases has since soared, raising fears of a high mortality rate among the elderly, who are particularly vulnerable.
Despite the rise, the official figures show only five people died from Covid on Tuesday and two on Monday.
It has led to WHO emergencies chief Dr Ryan urging China to provide more information about the latest spread of the virus.
He said: "In China, what's been reported is relatively low numbers of cases in ICUs, but anecdotally ICUs are filling up.
"We've been saying this for weeks that this highly infectious virus was always going to be very hard to stop completely, with just public health and social measures."
Speaking during a weekly news conference in Geneva WHO chief Tedros Adhanom Ghebreyesus said he is "very concerned over the evolving situation in China".
He appealed for specific data on disease severity, hospital admissions and intensive care requirements.
Dr Ryan added that "vaccination is the exit strategy" to coronavirus outbreaks.
China has developed and produced its own vaccines, which have been shown to be less effective at protecting people against serious Covid illness and death than the mRNA vaccines used in much of the rest of the world.
His comments come as the German government announced on Wednesday it had sent its first batch of BioNTech Covid-19 vaccines to China.
The German vaccines are to be administered initially to expats in China – estimated to be about 20,000.
It is the first foreign Covid-19 vaccine to be delivered to China, although no details have been released about the time or the size of the delivery.
Last month during a visit to Beijing, Chancellor Olaf Scholz pressed for the vaccine to be made freely available to Chinese citizens as well.
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