The World Health Organization said on Wednesday that numbers showing a global rise in COVID-19 cases could signal a much bigger problem as some countries also reported a drop in regular testing rates.

The WHO said that after more than a month of decline, COVID-19 cases began rising worldwide last week, with lockdowns increasing in Asia and China's Jilin province to contain the outbreak.

A combination of factors caused the increases, including the highly transmissible Omicron variant and its subvariant BA.2, as well as the easing of public health and social measures, according to the WHO.

WHO Director-General Tedros Adhanom Ghebreyesus told reporters, "These increases are happening despite a reduction in testing numbers in some countries, meaning the cases we see are just the tip of the iceberg."

WHO officials said low vaccination rates in some countries, partly driven by "a huge amount of misinformation," explain the rise.

New infections jumped eight percent globally compared to the previous week, with 11 million new cases and just over 43,000 new deaths reported from March 7 to 13. This is the first increase since the end of January.

The biggest jump was in the WHO Western Pacific region, which includes South Korea and China, where cases rose by 25 percent and deaths by 27 percent.

Africa also saw a 12 percent rise in new cases and a 14 percent increase in deaths, while in Europe there was a 2 percent rise in cases but no jump in deaths.

Other regions reported declines in cases, including the Eastern Mediterranean region, although this region saw a 38 percent increase in deaths linked to a previous rise in infections.

A number of experts have raised concerns that Europe is facing another wave of coronavirus, with cases rising since early March in Austria, Germany, Switzerland, the Netherlands, and the United Kingdom.

Maria Van Kerkhove of the WHO said in a statement that BA.2 appears to be the most transmissible type so far.

However, there are no signs it causes more severe illness, and there is no evidence that any other new variants are driving the rise in cases.

The picture in European countries is not uniform. Denmark, for example, saw a brief peak in cases in the first half of February, driven by BA.2, which quickly subsided.

But experts have begun warning that the United States may soon see a similar wave to that observed in Europe, potentially driven by BA.2, the lifting of restrictions, and the possible waning of immunity from vaccines given several months ago.

Antonella Viola, a professor of immunology at the University of Padua in Italy, said: "I agree with the easing of restrictions because you can't think of it as an emergency anymore after two years."

"We just need to avoid thinking that COVID is gone, thus maintaining the very necessary measures, which essentially consist of continuous monitoring and tracking of cases, and maintaining adherence to mask-wearing in indoor or very crowded places."

Editing: Dima Abu Khair