The global total of deaths passed 500,000 on Sunday, according to a New York Times database, while the number of confirmed cases surpassed 10 million.

The grim markers were hit as countries around the world struggle to keep new infections from reaching runaway levels while simultaneously trying to emerge from painful lockdowns.

In April, roughly a month after the World Health Organization declared the outbreak a pandemic, deaths topped 100,000. In early May, the figure climbed to 250,000. Now it has doubled in less than two months.

More than a quarter of all known deaths have been in the United States.

The number of confirmed infections — which took about 40 days to double — may be substantially underestimated, public health officials say. Data released last week by the Centers for Disease Control and Prevention indicated that the actual figures in many regions are probably 10 times as high as reported.

The Times has also found underestimates in the official death tallies in the United States and in more than a dozen other countries. Limited testing availability has often made it difficult to confirm that the virus was the cause of death.

In the United States, early hot spots emerged in the Northeast, particularly the New York metropolitan area, but the recent surge has occurred primarily in the South and the West, forcing some states to retreat from reopening plans.

Other countries, particularly Brazil and India, are also being hit with a large wave of new infections.

And while dozens of countries that took early steps to contain and track the pandemic have been able to control the virus within their borders, experts fear that fatigue with lockdowns and social distancing has allowed the virus to spread with renewed intensity across many corners of the world.