Sun Yixiao is pictured studying at his classroom, Oct 29, 2016. [Photo by Tian Xuefei/China Daily]

A teenager in Harbin, Heilongjiang province, has been praised for keeping his cool and getting on with his homework despite being trapped in an elevator for five hours.

Sun Yixiao, who is in his third year of junior high school, became trapped after the elevator in his apartment building shuddered to a stop around the fourth floor.

He tried all the buttons and called for help, even pushing a note through a gap in the door — but no one responded "probably because the other elevator was functioning normally and there is only one resident on the fourth floor," he said.

Realizing he might be trapped for some time, Sun took out his homework and began working on his assignments by the still-functioning light inside the elevator.

"Frankly I'd done all that I could do," he said. "All there left for me was to wait."

He started with mathematics, then completed his Chinese and physics homework, before moving on to some recitation assignments.

By the time he was rescued after five hours in the elevator, he had finished all his work.

His mother, noticing his absence, had organized a search party along with his teachers and friends.

Soon, news of Sun's ordeal began to spread across social media, and he was dubbed "Brother Calm".

But he said he wouldn't do his homework if he became trapped in an elevator again.

"I was too immersed in my work to notice my mother yelling for me," he said. "I would focus on getting out earlier next time."

His mother, Sun Hongyan, was relieved. "Perhaps he get his calmness after me," she said.

The boy's teachers said he has always been a good student and praised his time-management skills. "He's a very positive boy with good organizational abilities," said Cong Lin, Sun's class monitor.

Sun sees the incident as a chance to know himself better. "I realized something I didn't know about myself — I am practical, which makes sense as I also like physics experiments," he said.

"I'll try to take advantage of my practical abilities. Maybe one day I can study physics at Harvard."