Rescuers search for survivors after thermal scans indicate breathing and heartbeats beneath debris.

At least four people have been killed and 17 are missing after a building under construction collapsed in the Philippines, authorities say as search and rescue efforts are under way.

Rescuers retrieved at least three people on Monday from the rubble of the nine-storey building in the city of Angeles, north of the capital, Manila.

One of the victims had a pulse when he was retrieved but later died while another suffered cardiac arrest while still trapped, Maria Leah Sajili, an information officer at the Bureau of Fire Protection, said in a phone interview with the Reuters news agency.

Crews pulled the body of another person from the rubble, but it was not immediately clear if the unidentified body belonged to a person listed among the missing, rescuers said in an updated toll.

Due to that uncertainty, authorities said about 17 people were still considered missing, mostly construction workers who were sleeping at the building site when the disaster struck on Sunday.

The fourth person killed was a Malaysian tourist trapped in a budget inn, part of which was hit by an avalanche of debris from the collapsed building. Another guest at the inn was injured but managed to dash out, officials said.

At least 26 people have been rescued from the site.

Reporting from Angeles, Al Jazeera’s Barnaby Lo said hopes of finding more survivors were beginning to fade.

“Authorities are still saying the operation is a search and rescue. They will be using thermal detectors to try and find more signs of life, but if they don’t, they’re saying they will start using heavy equipment to clear the debris and retrieve people they believe are trapped under the rubble,” he said.

Officials said up to 70 people were employed at the construction site although most had gone home for the weekend.

Alfredo Albis, 55, told the AFP news agency he was asleep in a barracks for workers about 5 metres (16ft) from the structure when it gave way.

“I have two cousins who are still trapped there. They were working here to earn for their families and are missing,” he said, adding: “There’s a possibility that my relatives are dead.”

Sajili said: “Rescue in [a] building collapse is very challenging since any sudden shift triggered by the movements of our rescuers can cause areas to move and people under can get crushed.”

Sudden movements “may also bury our responders”, she said, explaining why this phase of the operation has to be done mostly manually.

If no more survivors are found, mechanical diggers and other heavy equipment will be brought in to clear debris and recover bodies, she said, but gave no timeline.

The cause of the collapse was not immediately clear.

Angeles Mayor Carmelo Lazatin told reporters that authorities were trying to locate the building owner to get answers, including clarity on the number of workers at the site.

Families have grown increasingly impatient and frustrated with the pace of the search and rescue operations.

Lea Casilao, 47, who travelled from Manila, said she only wants regular updates about the status of her husband, a construction worker believed to be trapped beneath the rubble.

“My youngest child keeps asking, but I do not have answers,” she said.