The World Health Organization has warned that the coronavirus pandemic will be lengthy and could lead to "response fatigue".

Six months after the United Nations agency declared a global emergency, the novel coronavirus has killed more than 680,000 people and infected more than 17.9 million, according to a tally by AFP. In South Africa the case count has topped 500,000.

The effects of the pandemic "will be felt for decades to come", the WHO said.

The Emergency Committee on COVID-19, convened by the WHO Director-General Tedros Adhanom Ghebreyesus, held its fourth meeting via video link on Friday. The committee includes about 30 members and advisers from around the world.

In a statement issued on Saturday, the committee expressed appreciation for the efforts of the WHO and its partners, but highlighted the expected lengthy duration of the pandemic. It noted the importance of sustained community, national, regional and global response efforts.

"The pandemic is a once-in-a-century health crisis, the effects of which will be felt for decades to come," Tedros told the committee.

Many countries that believed they were past the worst are now grappling with new outbreaks. Some that were less affected in the earliest weeks are now seeing escalating numbers of cases and deaths. And some that had large outbreaks have brought them under control, Tedros said.

The committee agreed that the outbreak still constitutes "a public health emergency of international concern". It will reconvene again within three months at the discretion of Tedros.

Tedros declared the emergency, WHO's highest level of alarm under International Health Regulations (2005) on Jan 30, when there were fewer than 100 cases and no deaths outside China.

The Americas continue to be the global epicenter, accounting for more than half the global total both in accumulated and new cases and deaths.

Death toll rises

The United States, the hardest-hit country, has had more than 4.6 million. Mexico overtook Britain to become the third hardest-hit country in virus deaths after Brazil and the US, with more than 46,600 deaths.

European countries, which have in the past few weeks had a resurgence of new cases after several rounds of easing lockdown restrictions and opening borders, are taking a step back to control the spread of the virus.

On Saturday Belgium required people traveling abroad for more than 48 hours to fill a passenger locator form online before returning to the country. The rules also apply to foreigners who enter Belgium for at least 48 hours.

Belgium last week imposed more stringent rules for mask wearing and night hours for bars and restaurants.

On Saturday thousands of people protested in the German capital, Berlin, against government COVID-19 restrictions, the BBC reported. Protesters said measures including the wearing of face masks violated their rights and freedoms.

Police broke up the demonstration, accusing organizers of not respecting COVID-19 hygiene regulations.

Germany has had one of the best COVID-19 responses in Europe, but it has also had a rise in the number of cases and deaths recently. It has more than 209,000 confirmed cases as of Sunday, according to the WHO.

Agencies contributed to this story.