Confirmed coronavirus cases in the United States hit three million

The number of confirmed cases of coronavirus in the United States has hit three million, according to the count kept by Johns Hopkins University.

But US health officials say the real number of infections is probably 10 times higher, or close to 10% of the population.

The numbers have been surging in recent weeks amid a rapid expansion in testing. But experts say the rise cannot be explained as just the result of more testing.

They say the outbreak is worsening, as shown by such warning signs as an increase in the percentage of tests coming back positive for the virus.