New coronavirus cases and hospitalizations are spiking in several US states, including Arizona, where state health officials have urged hospitals to activate emergency measures, and in California, where officials have placed nine counties with half the state's population on a watch list.

Since Memorial Day weekend (May 23-25), hospitalizations due to coronavirus infections have increased in at least seven other states: North and South Carolina, Oregon, Arkansas, Mississippi, Utah and Texas, according to The Washington Post.

Texas, one of the first states to loosen restrictions, reported the number of new coronavirus infections has climbed 71 percent across the state in the last two weeks. Texas officials have attributed the spike to hotspots such as meatpacking plants and state prisons, which have recently begun mass testing.

Arizona's state health department confirmed Tuesday that there have been 28,296 cases of COVID-19 in the state — an increase of 618 new cases since Monday. At its peak, Arizona's intensive care unit beds were 78 percent in use. As of Monday, 76 percent were occupied.

"We know COVID-19 is still in our community, and we expect to see increased cases," the Arizona Department of Health Services tweeted Tuesday night.

In Arizona, over the Memorial Day weekend, large crowds packed beaches in the state, especially at the popular Lake Havasu. In April, thousands of residents signed a petition to close the lake, concerned that tourists could bring the coronavirus with them and overwhelm area hospitals.

California has seen an uptick in cases in the past five days, according to numbers from Johns Hopkins University. More than 18 million of the state's 39 million residents live in counties now on the watch list, which includes Santa Clara and Fresno counties, according to Reuters.

Being on the watch list gives a county 14 days to contain its transmission and hospitalization rates. If a county makes insufficient progress, the state public health office may act.

This week, new daily confirmed cases of COVID-19 hit a new high across the state, topping 3,000 for the second time in a week and contributing to the 115,000 cases and more than 4,300 deaths the state has reported since the pandemic began.

"Many of the cases that are showing up in hospitals are linked to gatherings that are taking place in homes — birthday parties and funerals," said Olivia Kasirye, public health director of Sacramento County, one of the nine counties on the state watch list that may eventually be required to roll back reopening efforts.

On Tuesday, White House health adviser Dr Anthony Fauci said that the pandemic in the US "isn't over yet". He said vaccines will be the only way to stop the spread of the virus.

On Wednesday, The Wall Street Journal reported that the federal government plans to fund and conduct trials of three experimental vaccines starting this summer.

A vaccine by Moderna Inc will be first, starting in July, followed in August by one co-developed by Oxford University and AstraZeneca. In September, Johnson & Johnson's vaccine will begin trials.

Jon Huntsman, the former US ambassador to Russia and China and a current gubernatorial candidate in Utah, announced Wednesday that he tested positive for coronavirus.

Huntsman said he previously tested negative, only to receive a call telling him he was given the wrong results due to a faulty sample. After retaking the test, he tested positive. Huntsman said his family was also tested.

The former Republican presidential candidate faces steep competition in the primary election, which is on June 30. The Salt Lake Tribune reported that Huntsman is polling neck-and-neck with Lieutenant Governor Spencer Cox in the crowded four-person Republican field.

The Republican National Committee is expected to choose Jacksonville, Florida, as the new location for the main events of its national convention in August, according to various media reports Wednesday.

Two years ago, the party chose Charlotte, North Carolina, but state officials there declined to promise the Republicans a packed arena for their Aug 24-27 convention, citing public health concerns.

President Donald Trump has said he wants to accept his party's nomination before an enormous crowd, so his party sought a location that wouldn't insist on face coverings and social distancing.

The convention's more routine and lower-profile meetings still would take place in Charlotte to honor the party's contractual obligation to hold its convention in North Carolina and shield it from lawsuits for moving the banner events elsewhere.