The last Monday of May marks Memorial Day in the U.S.

It's a day to honor those who have died while serving in the U.S. military and with most states easing COVID-19 restrictions, many Americans could celebrate. 

U.S. President Donald Trump and first lady Melania Trump participated in a wreath-laying ceremony at the Tomb of the Unknowns at Arlington National Cemetery, outside Washington, D.C.

Due to COVID-19, only staff and family members with a pass to visit a gravesite could enter the cemetery. Elsewhere across the country, beaches, entertainment venues and other gathering spaces have reopened.

In some cases, large crowds gathered with many people not wearing masks.

Health officials are urging people to keep following COVID-19 guidelines. 

In a White House briefing on Sunday, coronavirus task force coordinator Dr. Deborah Birx said she was "very concerned" about people neglecting social distancing.

Experts are also warning of a possible second wave of COVID-19 cases if people stop following safety guidelines.

Some states are seeing an increase in cases after reopening communities. 

While other locations, like Washington, D.C., are seeing spikes while still under lockdown. 

White House guidelines suggest states should track a 14-day decline in COVID-19 cases before opening up, though many states have chosen not to follow the guidance.

Washington, D.C., cases spiked over the weekend, breaking a 12-day streak of declines and causing the city to "reset" to day 11, according to LaQuandra Nesbitt, director of the D.C. health department.

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