Greek firefighters recovered the bodies of 18 people on Tuesday who they believe may be migrants in the Evros region of northern Greece, close to the city of Alexandroupolis, where a major wildfire was burning for a fourth day.

The charred remains were found near a shack on the border of the Dadia Forest, a spokesman for the Greek fire service, Yiannis Artopios, said in a televised briefing. There have been no reports of missing people in the area, so the authorities said they were examining the possibility that the dead “had entered the country illegally,” Mr. Artopios said.

No further details were available about the dead. The Evros region, where the bodies were found, is on the border with Turkey and is a crossing point for thousands of migrants seeking to enter Europe through Greece.

Greek firefighters were battling several fires across the country on Tuesday, but their efforts were hampered by strong winds and dry conditions after a summer of back-to-back heat waves. In addition to the large fire near Alexandroupolis, firefighters were grappling with another blaze in the northern region of Rodopi, as well as blazes in Aspropyrgos and Fyli, west of Athens. Three villages near Fyli were evacuated in the afternoon as well as a monastery. And fires were burning on the islands of Kythnos and Evia.

And in neighboring Turkey, at least six villages are evacuated in the west, after forest fires broke in the province of Canakkale, an Aegean city along Dardanelles Strait, Turkish authorities said.

Vessel traffic on the waterway was temporarily suspended from south to north, the transportation ministry said, according to media reports.

The fire in Evros and those west of Athens were the most dangerous, Mr. Artopios told Greek state television, adding that 65 wildfires had broken out in just one day: “New fronts keep breaking out across the country.” In a briefing later, he said 93 fires had started in the past 24 hours.

A convoy of military vehicles was dispatched to northern Greece on Tuesday to help fight the fires there.

The European Union, which maintains a standing firefighting force pooled from member nations, dispatched more resources to Greece on Tuesday. The help includes 58 firefighters, a Black Hawk helicopter, nine water tanks and five airplanes, including two water-scooping aircraft from Sweden.

The fire service spokesman said that the authorities had sent several evacuation alerts since Monday to cellphones registered with both Greek and foreign networks in the Evros region. He added that the Greek police had mobilized a team of specialists to identify the victims.

As the flames spread in the early afternoon, the authorities in Alexandroupolis called for residents of 10 villages to leave. That followed the evacuation of dozens of hospital patients, some of whom were put onto a ferry in the early hours of the morning, while others were taken by ambulance. Most were being transferred to the northern city of Kavala.

Video from the early hours of Tuesday showed the sky glowing red behind the Alexandroupolis university hospital after the flames reached its grounds.

On the ferry, patients with IV drips lay on mattresses as nurses walked among oxygen tanks and other equipment, video showed. Εleven newborns from the same hospital were among those transferred.

Amid the chaos of the fires, police in Alexandroupolis said on Tuesday evening that they had arrested the owner of a truck who had locked 13 migrants in the trailer of the vehicle and posted a video of the episode on social media earlier in the day that showed him cursing and jeering at the migrants, all Syrian and Pakistani nationals.

The man, identified only as a “foreign national,” was arrested along with two Greeks believed to have “participated in the incident,” the police said. In the video, which spread on Greek social media, a man can be seen opening the door of the truck’s trailer to reveal the terrified faces of a group of migrants who appeared to be unharmed.

“They’re going to burn us, they’re going to burn us,” the man can be heard saying. “Twenty-five pieces,” he adds, musing a slur.

It was unclear what the “pieces” referred to, though another video posted to social media on Tuesday, featuring a man with a similar voice, shows makeshift incendiary devices in wooded areas, with comments suggesting that migrants had planted them there. “Look what they’ve done,” he can be heard saying. “They’re going to burn us.”

The man, identified by the police only as a “foreign national,” was arrested, along with two Greeks believed to have “participated in the incident,” the police said.

Earlier in the summer, wildfires hit the tourist destinations of Corfu, Evia and Rhodes. The fire in Rhodes led to massive evacuations, and thousands of tourists scrambled to leave.

On Monday, the authorities linked two more deaths to the fires after the charred body of a shepherd was found in the central Viotia region and the remains of a man believed to be a migrant was discovered in Lefkimmi, near Alexandroupolis.

Matina Stevis-Gridneff contributed reporting from Brussels, and Safak Timur from Istanbul.