Coronavirus is infecting more young people in their 20s and 30s in the South: Health officials say there has been a 'radical shift' as cases continue to spike in Florida, South Carolina, Texas and other southern states (9 Pics)

Authorities across the Southern United States are warning of worrying signs of young people becoming more susceptible to coronavirus, amid suggestions that lax social distancing and the reopening of bars is to blame.

Health officials and lawmakers in Florida, South Carolina, Georgia, Texas and Mississippi are all reporting spikes in the number of people in their 20s and 30s getting infected.

From the beginning of the pandemic up through May 30, the median age of positive coronavirus cases was 48, the Centers for Disease Control and Prevention (CDC) said. 

In several Southern states that average age is dropping. 

Crowds of young people unconcerned about COVID-19 flocked to Florida's beaches in May

A group of friends hang out on Miami Beach on Friday, as Florida sees a surge in COVID cases

Older people are still more likely to suffer severe effects of the virus, but the trend of young people getting infected is deeply troubling.

In Florida, which pushed hard to reopen quickly, Governor Ron DeSantis said Friday that the median age was 37 for newly diagnosed coronavirus cases over the last week. 

In the state, 62 per cent of new cases for the week of June 7 are under 45 years old, he said.

'That is a big change from where we were at the end of March and the beginning of April,' he said. 

'It was skewing much older at that time.'

The latest figures, as of Sunday

A day later he was even more emphatic, saying the state was seeing case loads 'shifting in a radical direction' toward populations in their 20s and 30s.

'We're also seeing that not only are they testing positive because they're testing more, they're also testing positive at a higher rate increasingly over the last week,' he said, adding there's evidence of transmission between those younger groups.

St Petersburg Mayor Rick Kriseman scolded millennials for their role in spreading the virus, saying, 'It is time that your generation started taking this more seriously.' 

Ken Welch, a county commissioner in Pinellas County, Florida, said they were working on ways to get the message across to a younger audience.

'One idea is to reach out to local sports figures like the Tampa Bay Buccaneers, the Lightning, the Rays, and have them talk about why it's important to wear a mask and why it's cool,' he said. 

'I'd love to see Tom Brady in a mask.'

On Saturday, Florida reported 4,049 new cases - the most reported in a single day. 

Andrew Cuomo, the governor of New York, has mused about stopping flights from Florida to his state.  

The number of coronavirus deaths, day by day. The trend is down but with worrying spikes

Greg Abbott, the governor of Texas, said last week that people under 30 made up a majority of new coronavirus cases in several counties. 

He said that increase in young infected people could be related to Memorial Day parties, visits to bars or other gatherings.

In Galveston County, Texas, Dr Philip Keiser with the local health department told CNN affiliate KPRC they were seeing a lot of infections in young people. 

'Our average age last week of people that were positive was age 30, the average age of people getting tested was 47,' he said.

Cell phone data from the county showed that less than 7 per cent of people were still social distancing, he said.

Visitors to Six Flag Fiesta Texas enjoy the ride on Friday, amid mounting concern about COVID

Twelve bars in Texan cities including Houston, Dallas, Fort Worth, and Austin have had their permits revoked for 30 days for violating COVID-19 protocols.

In Brownsville, Texas, Dr Joseph McCormick, an epidemiologist with the UT Health School of Public Health, said new infections in people under 35 have shot up dramatically, accounting for more than half of the recent cases in his region.

'We are seeing a resurgence of transmission, and it's being driven by younger people,' he told NPR. 

He said that older people still make up the bulk of hospitalizations.

Crowded beaches and bars at the nearby resort town is 'pretty clear evidence' of why younger adults are the ones getting sick in his community, McCormick said. 

'This is relatively new, and I think it's because that segment of the population decided, "OK, I'm free," whereas the older group is thinking, "Woah, wait a minute, I'm still in jeopardy."'

Officials in one Texas county even link the spike in cases to young people floating in the river. 

Bars in Texas, such as the one in an image from the licensing authorities, have been shut down

Almost 2.3 million people in the United States have been infected, making it the hardest-hit country by far. Britain and Brazil are coming in second and third place worldwide

Young people in Texas have been flocking to bars like this one, which was closed for 30 days

In South Carolina, health officials said Friday people under the age of 30 were increasingly testing positive for the virus.

Now around 18 per cent of the state's total cases come from people between the ages of 21 and 30, CNN reported.

'The increases that we're seeing serve as a warning that young adults and youth are not immune to Covid-19,' said Dr Brannon Traxler, the state's Department of Health and Environmental Control physician consultant. 

'They also tell us that younger South Carolinians are not taking social distancing seriously.'

In Mississippi, where social distancing was described as 'overwhelmingly disappointing,' officials attributed clusters of new cases to fraternity rush parties. 

In California, 44 per cent of recent coronavirus cases occurred in those under the age of 35, according to a study by George Lemp, director of the University of California's HIV/AIDS Research Program. 

Young people in Georgia flocked to the beaches and held parties over Memorial Day

And a senior medical official at Georgia's largest hospital said the new trend 'frightens' him.  

The hospital reported seeing an increase in patients in their 20s and 30s, according to CNN affiliate WSB.

'It's a little bit of a disturbing trend, and what frightens me is not only that they are younger, the potential of them infecting other people, particularly parents and grandparents,' said Dr Robert Jansen, chief medical officer at Grady Health System.

Data from Johns Hopkins University showed that at least 23 states are trending upward in new cases compared to last week. 

Ten of those states reported more than a 50 per cent jump -  including Texas and Florida, which were some of the first states to begin reopening.