Rescuers in Beirut said they detected a possible heartbeat under the rubble of a building destroyed by the blast on August 4.
A sniffer dog reportedly alerted rescuers to the presence of a potential survivor, sparking a major search.
If someone was found alive, it would mean that the person has been stuck under the wreckage for 29 days.
Specialist sensor equipment has been brought to the Mar Mikhael area following unconfirmed reports that a heartbeat was detected.
“These (signs of breathing and pulse) along with the temperature sensor means there is a possibility of life,” rescue worker Eddy Bitar told reporters at the scene.
He added a civil defence unit had been called in to help with extra equipment to conduct the search.
Rescue workers in bright jackets clambered over the building that had collapsed in the blast.
Crowds gathered around the building while the search and rescue team dig through the rubble to locate the source of the heartbeat.
Local media said any search and rescue effort, if it became clear that someone was still alive, was likely to take hours.
The Chilean rescue team involved in the search arrived in Lebanon three days ago to help sort through the wreckage.
The same team reportedly rescued a man in Haiti 27 days after he was trapped by an earthquake, according to the Daily Star.
BBC journalist Claire Read tweeted: “Whispers of ‘Is it true? Could someone be alive??’ One month tomorrow since Beirut blast. The crowd is buzzing and the rescuers hush us as they listen and search.”
Photos from the scene show members of the military standing with workers in high-vis jackets as they inspect the wreckage.
Members of the public, most wearing face masks, can be seen filming on their phones.
According to Lebanese Health Ministry, at least 190 people were killed and more than 6,000 injured in the Beirut blast that devastated the port area a month ago.
More than 300,000 people are now facing homelessness after the disaster.
Less than a week after the explosion, Lebanon’s government stepped down.
Prime Minister Hassan Diab addressed the nation, announcing his resignation and that of his government in the wake of the blast, which he called a “disaster beyond measure.”
He criticised Lebanon’s ruling political elite for fostering what he called “an apparatus of corruption bigger than the state.”
“We have fought valiantly and with dignity,” he said, referring to members of his cabinet.
“Between us and change is big powerful barrier.”
Diab compared Tuesday’s explosion to an “earthquake that rocked the country” prompting his government to resign.
“We have decided to stand with the people,” he said.
Three cabinet ministers had already quit, along with seven members of parliament.
After the blast, protests took place in the city asking the Government to step down.