US President Joe Biden announced on Tuesday his administration is boosting the weekly supply of vaccines to states and territories by 16% next week.

He added he hopes to have enough doses to vaccinate 300 million Americans by the end of the summer or early fall.

"This will be one of the most difficult operational challenges we've ever undertaken as a nation," Biden said about the effort to distribute vaccines, according to CBS News. He also said he plans to give governors more advance notice on forthcoming allocations of the shots, adding that the vaccine distribution process established by the Trump administration was "in worse shape than we anticipated."

Vaccine supply to states, territories and Indian tribes will climb to 10 million doses next week, up from 8.6 million and continue at that rate for the next three weeks.

Governors will be given a three-week forecast of their vaccine allocations, giving them more time to prepare vaccine distribution plans.

"We will both increase the supply in the short term by more than 15% and give our state and local partners more certainty about when the deliveries will arrive," said Biden, who called vaccine distribution a "wartime effort".

The president claimed there will be enough vaccine to fully vaccinate 300 million Americans "by end of the summer, beginning of the fall." At the same time, he urged Americans to continue to follow coronavirus guidelines, such as wearing a mask.

"Our plan will take time. Despite our best intentions, we're going to face setbacks," said Biden.

The United States several days ago surpassed the 25 million mark in cases of COVID-19.

The confirmed coronavirus death toll in the US topped 400,000 last Tuesday, just one day before Biden took the oath of office.