Ukraine's SBU security service said drones on Friday had again struck the sea port and refinery that make Tuapse an important hub for Russian oil exports.
Reuters could not confirm the latest strike on the refinery, which has been hit and set ablaze at least twice since April 16 in previous attacks that have halted production.
Local Russian officials said a major operation was under way to put out a fire at the sea port.
The attacks have thrown up dense black clouds over the town and caused oil slicks along the coastline, ruining the beaches of the popular resort.
They are part of what President Volodymyr Zelenskiy said was a Ukrainian strategy to disrupt Russia's huge energy industry and knock key sites out of operation for as long as possible.
He posted on X that these operations had slashed at least $US7 billion ($A9.7 billion) since the start of the year from energy revenues that Russia uses to finance the war.
It was not possible to independently confirm that figure. Moscow, on the other hand, stands to reap a windfall in oil profits from rising global prices resulting from the war between the United States, Israel and Iran.
More than four years into their conflict, Russia and Ukraine have been pounding each other from the air, while frontlines on the battlefield remain largely static.
Throughout the war, Russia has frequently bombed Ukrainian power plants and the electricity grid. A Russian drone attack overnight damaged port infrastructure in Ukraine's southern Odesa region and wounded two people, the regional governor said. A daytime drone attack on Ternopil, in Ukraine's far west, hit industrial facilities and injured 10 people, the mayor said.
Residents of Tuapse have been warned to stay inside, keep their windows closed, and drink only bottled water as authorities try to foster a sense of solidarity.
"Today, in these difficult days, we are overcoming adversity and solving important problems together. And I believe we will succeed!" district head Sergei Boiko said in a message congratulating residents on the May Day public holiday.
Less than three hours later, he published a renewed drone alert, telling people to take shelter in windowless rooms.
The town has been subject to a state of emergency since Tuesday, when an attack started a huge fire at the refinery that was not extinguished until two days later.
Authorities said on Friday that they had so far cleared more than 13,300 cubic metres of fuel oil and contaminated soil along the coast.
State TV showed a reporter standing on a blackened beach and using a spade to show how deep the oozing filth had seeped.
In an online chatroom, some locals vented anger and despair, criticising what they saw as a lack of effective action from the central authorities in Moscow.
"Who wants to get cancer? Who wants their children to get sick? Or maybe someone wants to burn to death in their bed from a drone explosion?" one woman wrote.
Another posted that the pollution would linger for years.
"It will impact people's health, our children's health, the environment, and the future of the town. All of this could have been avoided. But someone's ambitions and decisions once again proved more important than our safety."
