SYDNEY, Australia — Already besieged by one of the worst wildfire seasons in Australian history, evacuees and those staying put on Friday braced for conditions to grow even more dire.

Across Australia’s southeast, supermarket shelves emptied, gas stations closed and roads became clogged with traffic as skies turned a hellish red or a smoke-choked white. Firefighters were overwhelmed by more than 100 raging blazes and families were forced to make perilous stay-or-go decisions.

The toll so far includes 18 deaths, more than 1,000 homes destroyed and thousands of animals killed. On Friday, experts and government officials offered a grim warning: The upcoming weekend is likely to be the most dangerous yet.

Predictions for Saturday

Early Friday, the New South Wales Rural Fire Service dramatically expanded its estimate of the amount of land at risk from spreading fires, including “ember attacks,” in which burning wood fragments are carried by wind. The weekend is expected to bring high winds and temperatures over 100 degrees Fahrenheit, or about 38 Celsius.

About 4,000 people, including about 3,000 tourists, were trapped in the town, according to the Australian Broadcasting Corporation.

Some people would be unable to board the ships because it required using ropes to get on board, ABC reported. Those who made it onto a ship will take a 17-hour voyage to get to Melbourne.

‘It feels like it’s not real’

People staying behind on the south coast were preparing for the worst, after days of dwindling resources.

Clarinda Campbell, 37, said she and her two children had been without power and had barely slept since Tuesday, when fires swept through the area. They fled to a property owned by her parents in Surf Beach, where phone reception was out in all but a few spots. Water and food sources were running low, with no way to store them, and there was no garbage disposal service. Radio was the main source of information, and shops were accepting only cash.

But the community rallied together, she said. On Friday, a neighbor brought fresh bread, which is now a luxury.

“It has been very touching,” Ms. Campbell said. “In the crisis you see the best and the worst.”

On Friday, the family fueled up their cars in case a getaway was necessary.

Without the use of phones, they had to make contingency plans. Ms. Campbell said she was nervously waiting for Saturday, when her husband, who had stayed behind in the town of Broulee to defend their home, was supposed to run to a nearby hilltop with a sliver of cellular reception, to let her know if he was safe.

But with the possibility of fires blocking escape routes, she was trying to reach her husband on Friday to persuade him to leave.

“It feels like it’s not real,” she said. “I’ve gone to sleep every night and woken up every morning hoping that it was just a bad dream.”

Bernard Kreet, a caterer in Catalina, said he was hosting two families who had been evacuated from other towns, thinking that Catalina would probably avoid the worst. While his partner had left for the next town north, Mr. Kreet opted to stay behind.

“It’s so hard to get out of town, it’s chaos down here,” he said.

Catalina has run out of rice and fuel is low, he said. Power was out from Tuesday to Thursday.

When fire swept close to the area on Tuesday, he huddled with about 300 others at a Catalina golf club, waiting to hear if it would come their way.

“The feeling in that room, of 300 people just frightened — it was heavy,” he said. “There will be so many people with PTSD after this. So many people are just so anxious.”