Friday marked a dark day in Ukraine's months-long turmoil, with forces sent by the government in Kiev clashing with pro-Russian separatists in the breakaway town of Slovyansk, leaving at least three people dead after two Ukrainian helicopters were reportedly shot down.

Unrest also broke out away from the battle zones of eastern Ukraine. In Odessa, the country's third-largest city, pro-Kiev and pro-Russian demonstrators fought in the streets, hurling rocks, loose flagstones and Molotov cocktails as overwhelmed riot police beat a hasty retreat. Rival protest camps have existed for months in public spaces in the city, though no fracas in the recent past can match this round of violence.

It kicked off after marchers calling for Ukrainian national unity, which the Kyiv Post claims was largely comprised of supporters of the local soccer team, encountered a rival pro-Russian group. Barricades were set up and buildings set aflame. Initial reports suggest that dozens were wounded, with at least three people shot dead, according to police. Then, police said at least 31 people were dead after pro-Kiev demonstrators hurled Molotov cocktails into a building where a pro-Russia contingent was holding out.

Journalist Howard Amos, in Odessa on Friday, chronicled the violence on his Twitter feed:

The first floor of the regional administration building seems to be ablaze: pic.twitter.com/tE6D5g1EAd — Howard Amos (@howardamos) May 2, 2014

Chaos in #Odessa, thousands now on streets - tho most watching. Molotovs, stones go back and forth: pic.twitter.com/8d1QBRR5CH — Howard Amos (@howardamos) May 2, 2014

As far as I can tell, the pro-Russian activists appear to be surrounded on 3 sides. Riot police nowhere to be seen: pic.twitter.com/E8dt49ataa — Howard Amos (@howardamos) May 2, 2014

Central Odessa a mess. Shark decoration got used in this barricade: pic.twitter.com/vFnOxWM2D9 — Howard Amos (@howardamos) May 2, 2014

These girls breaking up cobblestones for pro-Maidan side in #odessa say they are 14 years old: pic.twitter.com/K4WbCNC6Xq — Howard Amos (@howardamos) May 2, 2014

Amateur video from Odessa has also flooded social media:

Until now, Odessa, a famed Black Sea port, has existed somewhat at a remove from the chaos gripping Ukraine. But it was perhaps only a matter of time. The city has a rich history and was the crown jewel in Catherine the Great's settlement of the region, starting in the late 18th century after Tsarist Russia wrested control of the northern rim of the Black Sea from the Ottoman Empire. The "New Russia" or "Novorossiya" that she set out to establish — and which both authorities in Moscow and pro-Russia separatists now invoke — was centered on Odessa, an elegant, cosmopolitan city of colonnades and arches.

After the nearby Crimean peninsula was annexed by Russia in March, some thought Odessa would be the next to fall into Putin's crosshairs. But unlike Crimea, where a vast Russian majority seemed happy to align with Moscow, Odessa has a far more complicated identity. Even under the Tsars, the city — teeming with merchants and traders from all sorts of backgrounds — became difficult to rule, writes Brown University historian Patricia Herlihy:

By the mid-19th century, Russia was suspicious of the city because of its foreign population. Greeks, Bulgarians, Poles and Ukrainians formed secret societies. Jews made up an increasing percentage of the population. And Nicholas I, who ruled from 1825 to 1855, called Odessa "a nest of conspirators."... Worldly, materialistic, commercial, impudent, entrepreneurial and ethnically diverse, Odessa was an exceptionally cosmopolitan and non-Russian city.

That character lingers, perhaps. While Odessa was a base of support for the ousted Ukrainian President Viktor Yanukovych — whose departure precipitated the alarming series of escalations that have brought Ukraine and Russia to the precipice of war — there's clearly also a strong current of pro-Kiev feeling, fueled in part by the havoc elsewhere. It belies, says Volodymyr Dibrova, a Ukrainian teacher and writer at Harvard University, the crude divisions that have emerged, pitting "Russian-speakers" against Ukrainian nationalists and the provisional government in Kiev. "It was a Yanukovych stronghold," Dibrova said, "but you see now when push comes to shove, in these times of crisis, that issues of language are secondary to other things — to [people wanting] rule of law, to common decency."

But given the scenes from Odessa today — where riot police fled and city residents battered each other — those two virtues now seem in short supply.

An earlier version of the story mistakenly identified the pro-Russia protesters in Odessa as being comprised largely of organized soccer fans. The soccer fans were in fact in the pro-Kiev ranks. The error has been amended.