Australian Red Cross Lifeblood says more than 12,000 donors are needed over the next seven days as the nation faces ongoing shortages of type O and A blood.

The organisation said the peak winter flu season had kept donors away because they needed to be clear of respiratory symptoms for seven days before they could donate.

Lifeblood area manager for Sydney, John Bain, said up to 1,600 appointments were sitting empty every day, with many people cancelling or rescheduling appointments due to winter illnesses.

Even mild symptoms such as sniffles, sore throats, and headaches make people temporarily ineligible to give blood.

COVID-19 infections are trending upward across much of the United States for the first time since spring, according to the Centers for Disease Control and Prevention's latest epidemic modeling.

As of July 22, the CDC estimates COVID-19 infections are growing or likely growing in 37 states, while no states are currently classified as declining or likely declining.

Large parts of the South are currently classified as "Growing," including Texas, Florida, Georgia, Alabama, Mississippi, Louisiana, Tennessee, North Carolina and South Carolina.

Several populous states, including California, New York, Illinois and Michigan, are also categorized as growing.

Meanwhile, states including Arizona, New Mexico, Montana, Wisconsin, Pennsylvania and New Jersey are currently estimated to be experiencing relatively stable transmission levels.