There have been previous reports of the militants threatening or killing Christians, but it is not yet known how many have died. The military says a total of 26 civilians have been killed, but the militants still control about a fifth of the city, and there may be other areas the military has not reached.
A propaganda video released by the Islamic State on Monday showed what was said to be the execution of six Christians in Marawi. However, it was not possible to verify that the scene was recorded there, and military officials cast doubt on the claim.
The three Christians who escaped Marawi were among a group of five laborers from Iligan City, about 25 miles to the north, who were hired to refurbish the house of a prominent Muslim trader in Marawi.
But what was supposed to be a routine job turned into a nightmare when they were trapped in hostile territory with Islamist militants hunting them down.
One of the men, Nick Andilig, 26, said about 50 militants suddenly appeared in the neighborhood where they were working, shouting “Allahu akbar” and displaying a black flag.
“They claimed to be ISIS out on a mission to cleanse the city,” he said, using another name for the Islamic State. He said he thought that meant they would kill all non-Muslims in the area.
The fighters appeared to be in their 20s, wore face masks and head gear, and carried long firearms, Mr. Andilig said. Some arrived in a police car, which they had apparently stolen.
Mr. Andilig said their employer hid the workers in his basement. When the militants reached his door, the workers overheard him arguing with them. “He told the gunmen that there were no Christians in the house,” Mr. Andilig said.
The militants eventually moved on to the next house. Then they heard shooting.
Mr. Andilig said he did not see the killings, but when he and his group eventually emerged from hiding, they saw several bodies on the ground with what appeared to be gunshot wounds.
“Our employer escaped earlier with another household staff,” he said. “He said he would come back for us but never made it. He was a good Muslim.”
That left the five workers, four men and a pregnant woman, trapped in the house.
For days they subsisted on food the owner had left behind, mostly canned goods and rice, but eventually that ran out. They began to leave the house on brief forays to scrounge for food, eating plants they found.
They were getting hungry, and the explosions outside, apparently from bombs dropped by military airplanes, had been getting louder, suggesting the bombs were getting closer.
“All of us decided to escape,” Mr. Andilig said. “But our companion, who is seven months pregnant, could not run along with us. She and her husband decided to stay.”
“We said we’d try to get rescue for them if we made it out. We also told ourselves that our fate was with the Lord.”
As dawn broke on Tuesday, Mr. Andilig, Mr. Torres and Arman Langilan, 22, fled.
“We told each other, whatever happens, happens,” Mr. Torres said. “If we get hit and die, that’s our fate. But we had to escape. Or at least die trying.”
They alternated running and hiding in thick shrubs, eventually reaching the Agos River that divides the city and separates the area controlled by the militants with that controlled by the Philippine military.
They tumbled down the banks of the river as bullets fired by snipers sporting black bandannas whizzed over their heads. They plunged into the rushing water, hugging the banks until they saw a clearing, and climbed out on the other side.
They were found by the police wandering, tired and hungry, among the ruins of the city, which the fighting has transformed into a desolate landscape of pockmarked buildings and cratered structures.
At a government checkpoint, they told their stories to the police and to The New York Times.
All showed signs of trauma. Mr. Langilan spoke incoherently and shuddered when bombs from a passing military plane exploded in the distance. Mr. Andilig clutched a piece of cucumber, his only real food in days, and repeatedly said he needed a shower.
Mr. Torres was still wearing pants and a shirt smeared with paint, the clothes he was wearing the day hostilities broke out.
The fate of the two colleagues they left behind remains unknown. Attempts to reach them by mobile phone have been futile.
Christians and Muslims have long coexisted peacefully in Marawi, Mr. Andilig said.
“I have many friends who are Muslim,” he said. “It was never a problem in the past.”
There was still evidence of that camaraderie at another neighborhood in Marawi, where five Muslim police officers hid and protected five Christian construction workers for nearly three weeks.
“We had our chance to flee because we are Muslims,” said Lumla Lidasan, one of the officers. “But as police officers we are mandated to protect the people. So we elected to stay because they will execute the Christian civilians.”
Officer Lidasan said he and his colleagues were armed with long rifles, which allowed them to keep the militants at bay while the Christians hid in the basement. Outside, he said, he heard rockets and bombs exploding as the city was reduced to rubble.
“They are not real Muslims,” he said. “Real Muslims will not hurt people unprovoked, regardless of religion.”
One of the Christians, Rodel Aleko, 24, said the bombing runs shook their hiding place, but whenever he peered out the window he would see the gunmen still patrolling.
A police officer, Ricky Alawi, said there were times that they thought it was going to be the end for all of them. He said they were in radio contact with the army, who told them that there would soon be a bombing run in their area. They decided to take a chance and leave that day, which was Monday.
“As we were fleeing we saw bodies lying on the ground,” he said. “The gunmen were shooting at us as we ran toward the next building, where we stayed overnight. One of my colleagues and one of the civilians were injured.”
When there was a lull in the fighting, the group started slowly walking toward Banggolo Bridge but were stopped by a gunman. Mr. Alawi said he told the militant that his colleagues were too traumatized to speak.
“He told us to just wait because he would call his companions,” Mr. Alawi said. “When he left, we ran as fast as we could and crossed the bridge.”
Mr. Aleko was wounded when bomb shrapnel hit his left leg, he said, and the blasts were so loud that they may have permanently damaged his hearing.
But he could only feel grateful.
“This is our second life,” he said. “I thank God for these officers.”