SINGAPORE - Holding back his emotions, Pastor Davy Sim entertained visitors, shared precious memories, and delivered a 20-minute sermon at the wake service of his 16-year-old son, Benjamin Sim Wen Ming, who died after a 2.4km run in school.

But when he was alone, Mr Sim, 55, struggled with the loss of his second child.

He told The Straits Times: "It is difficult when we are alone, when we are home; that is when memories of him just come flooding.

"It is not easy, but we are coping."

Mr Sim added that he was Benjamin's "stress reliever", someone the teen enjoyed relaxing with.

The Secondary 4 student of Chong Boon Secondary School had collapsed just after completing a run during his physical education lesson on Tuesday (Aug 1) morning.

At the wake at the Singapore Bible Baptist Church on Wednesday night, Mr Sim, who is a pastor at the church, shared that the family has to accept Benjamin's death. He said his son "had given lots of joy" to his family.

"This week has been overwhelming. Seeing my son in the casket, it is beyond words," he added.

"But I thank God. It is not a tragedy. It is a blessing because he is now in a better place, he is in heaven."

Mr Sim, who has an older son, described Benjamin as a sporty individual who, like him, was "a livewire".

"He was always cheerful and jovial," he said.

He shared that Benjamin had no history of any medical conditions.

More than 300 people, including church members, turned up at the wake at the Pasir Panjang Road church.

Benjamin's death left many of his peers devastated.

A schoolmate, who declined to be named, said that Benjamin was a keen athlete and a hardworking student.

"He was a good friend we looked up to," he said. "We will miss him. He is now in a better place."

The Straits Times understands that Benjamin had keeled over and hit his head on the ground near the school foyer after completing the run around the school in Ang Mo Kio.

The Singapore Civil Defence Force (SCDF) was alerted to the incident at 8.15am on Tuesday. A school staff member who reported the incident to the SCDF was already administering emergency resuscitation when a fire bike and an ambulance arrived at the scene.

As Benjamin was being taken to Tan Tock Seng Hospital, paramedics continued to administer cardiopulmonary resuscitation. He was later pronounced dead at the hospital.

Chong Boon Secondary principal Yeo Kuerk Heng had earlier said the school was "deeply saddened" by his death.

"Benjamin was well regarded and popular among his peers, and was especially known for his cheerful and friendly disposition," he said.

The boy, who had been a volleyball player on the school team for four years, was active in class. He was also good in English and would help his peers who were weaker in the subject.

School leaders, staff and counsellors are providing emotional support and assistance to Benjamin's family, affected students and staff.

Police are investigating the unnatural death.

Benjamin will be cremated on Friday at Mandai Crematorium.