A man suspected of setting a public bus on fire in northern China, burning 17 people to death, had told friends he planned violence, reports said Wednesday, citing social media postings in which he agonised over unpaid debts.

Police captured Ma Yongping, 33, Tuesday after the blaze engulfed the vehicle in flames in Yinchuan, the capital of remote Ningxia region.

A passenger on the bus said it went up almost instantly, giving them mere moments to scramble off.

"It came rushing with a sound like a spray of water. My shoes were burned off. The soles of my feet were roasted", the survivor told the Beijing News.

Ma, a college graduate who had studied in Japan, had accumulated more than 300,000 yuan ($46,000) in debts while a contractor on an engineering project, much of it salaries for his workers, according to an article on Chinese news site Sina which was removed shortly after it appeared on Wednesday.

The company refused to pay him, it said, and according to the Beijing Youth Daily, on the morning of the attack he sent a message to friends on chat application WeChat saying: "At a time when even a person's basic rights can't be guaranteed, he has a right to take action to fight for (them)."

He also posted a picture of a letter he had written in December.

"I can't understand how things came to this next step", he wrote. "I think I am not an impulsive person, nor am I a mental patient, even less am I a blood-thirsty terrorist. But why has this outcome come about?"

Under interrogation, Ma told police he purchased two jerry cans of petrol at a filling station and used a lighter to set the bus aflame, the Beijing Youth Daily reported.

Chinese citizens have sometimes turned to violence against innocents in attempts to publicise their plight after failing to obtain redress for low-level disputes.

In 2013 a man started a fire on a vehicle in Xiamen in the eastern province of Fujian, killing 47 people including himself, after writing online he had appealed unsuccessfully to local police 56 times over social security benefits.

The following month a wheelchair-bound man who complained for years about police brutality built a home-made bomb and set it off at Beijing's airport after handing out leaflets about his case.

dly/slb/mtp

SINA CORPORATION