Germany's health minister has expressed concern over a new COVID-19 subvariant linked to growing hospitalisations in the northeastern United States, adding that Berlin was watching the situation closely.

As much of the world looks to rising COVID cases in China, infectious disease experts have also been increasingly worried about the highly contagious Omicron XBB.1.5, which made up more than 40% of U.S. cases, official data showed last week.

"Hopefully we get through the winter before such a variant can spread among us," the minister, Karl Lauterbach, wrote on Twitter late on Wednesday.

"We are monitoring whether, and to what extent, XBB.1.5 occurs in Germany."

Seven of the 10 U.S. states to see rising infections and hospitalisations are in the Northeast, in line with higher XBB cases, Dr. Michael Osterholm, an infectious disease expert at the University of Minnesota, told Reuters in a recent interview. (Writing by Rachel More; Editing by Clarence Fernandez)