Update:

It appears that the alt-right "rally" ended hours ahead of schedule, thanks at least in part to the remarkable size of the counter-demonstration.

"Thousands of counter-protesters remain in Boston," noted Mic's Jack Smith. "The right-wing rally is totally empty."

"You couldn't even call it a rally," said Boston.com's Meghan Barr in an appearance on MSNBC.

Thousands of counter-protesters remain in Boston. The right wing rally is totally empty, hours before it was intended. pic.twitter.com/yzD7vygnHM — Jack Smith IV (@JackSmithIV) August 19, 2017

By contrast, some 40,000 people turned out for the counter-protests.

Earlier:

"I couldn't see the end of this crowd with binoculars," wrote freelance journalist Britni de la Cretaz after looking on at the sea of protesters gathered in Boston Saturday to counter a planned alt-right "free speech" rally.

According to the "Fight Supremacy" Facebook page, as many as 14,000 people said they were planning to attend the counter-protest—far exceeding the number of people expected at the alt-right event. As the Washington Post reports, the counter-rally could ultimately consist of 30,000 people.

ABC posted an aerial view of the march toward Boston Common:

Aerial view shows large crowd of counter-demonstrators marching through Boston ahead of planned "free speech" rally. https://t.co/30EmFLxYZU pic.twitter.com/RKpELfYccS — ABC News (@ABC) August 19, 2017

"As we have seen with the events in Charlottesville and around the country, white nationalists are emboldened by the current political administration and growing police state," wrote the organizers of the "Fight Supremacy" march. "Rallies and marches organized by white supremacists are more prevalent than in recent years, and—as always—it is the most marginalized who are left vulnerable."

The alt-right event comes just one week after the so-called "Unite the Right" rally in Charlottesville, Virginia which culminated in violence perpetrated by white supremacists, leaving one woman—Heather Heyer—dead and many more injured.

In Boston, activists with Black Lives Matter and other groups carried signs calling for love and peace over hatred and violence.

As people began to arrive at the scene of the rally, chants of "Shame!" were directed at the few gathered for the alt-right event:

The Calvary has arrived with chants of "Shame!" #fightsupremacy pic.twitter.com/qeC8aNnO8K — Sebastian Murdock (@SebastianMurdoc) August 19, 2017

According to Jack Smith of Mic, "The Boston counter-protest is now perhaps the largest anti-racist protest this year," and "many more" are still expected to arrive.