The police told Stomp that they were alerted to an accident involving a bus and a pedestrian along Choa Chu Kang Avenue 5 towards Choa Chu Kang Avenue 4 at 9.05am.
The unconscious boy was taken to National University Hospital where he subsequently succumbed to his injuries, a police spokesman said.
The boy was reportedly crossing the road when the accident occurred.
He was extracted from under the rear wheel of the bus by the Singapore Civil Defence Force using lifting equipment.
Ms Margaret Teo, SMRT's Vice-President for Corporate Communications, told Stomp: "We are sorry and sad that the accident has happened.
"Our care team has reached out to the boy's family at the hospital to provide support and assistance. Meanwhile, we are assisting the police in their investigations.
"We would also like to apologise to affected commuters."
The 57-year-old bus driver is assisting the police with investigations.
The police also urged members of the public not to circulate photos or videos of the deceased at the accident scene, out of respect for his family.