The head of the World Health Organization warned Friday of a resurgence of novel coronavirus infections in Europe and the United States, saying the northern hemisphere is "at a critical juncture."

"We are at a critical juncture in this pandemic, particularly in the northern hemisphere," WHO Director General Tedros Ghebreyesus told a press conference.

World Health Organization Director General Tedros Adhanom Ghebreyesus speaks at a press conference at its head office in Geneva on July 3, 2020. (Kyodo)

"The next few months are going to be very tough and some countries are on a dangerous track," the WHO chief said, urging leaders to take action "to prevent further unnecessary deaths, essential health services from collapsing and schools shutting again."

His remarks came as many European countries such as Britain and France are seeing an uptick in cases of COVID-19, the disease caused by the virus, after the relaxation of social distancing measures.

In the United States, the country hit with the world's highest number of infection cases and fatalities, many states have also reported a resurgence of infections as they move to reopen their economies.

"Too many countries are seeing an exponential increase in cases and that is now leading to hospitals and ICU running close or above capacity and we're still only in October," Tedros said.

Noting that oxygen is effective for saving patients with COVID-19, he said, "Many countries simply do not have enough oxygen available to assist sick patients as they struggle to breathe."

Tedros also stressed the need to narrow what he calls "the global oxygen gap," pointing out that some of the poorest countries are estimated to have less than 20 percent of the oxygen needed for COVID-19 patient care.

Global coronavirus cases have topped 42 million with deaths from COVID-19 reaching 1.14 million, according to Johns Hopkins University data.