An explosion at a Shanghai supplier to Apple Inc. injured 61 workers after aluminum dust produced by polishing cases for iPads ignited, China Labor Watch said.

The cause of the Dec. 17 blast at Ri Teng Computer Accessory (Shanghai) Co., owned by Taipei-based Pegatron Corp., was similar to that of an accident at a Foxconn Technology Group facility in May, according to an e-mailed statement from China Labor Watch yesterday. Pegatron Chief Financial Officer Charles Lin didn’t immediately return calls to his office seeking comment.

Foxconn, the biggest contract manufacturer for Apple, said in May “combustible dust” probably caused the May 20 accident at its factory in Chengdu, China, when three workers died and 15 were injured. Pegatron said Dec. 18 that some employees injured in the explosion the previous day were hospitalized, without providing details about the accident.

“We are working closely with Pegatron to understand the cause of this accident,” Carolyn Wu, a spokeswoman for Apple, said by telephone today. “Our hearts go out to the people who were hurt in Songjiang,” she said, declining to elaborate.

Local authorities in the Songjiang area of Shanghai have started investigating the accident at Ri Teng, the city government said in a Dec. 17 posting on the Sina Weibo microblogging service. No one answered the phone at the press office of the Shanghai government today when Bloomberg News called seeking comment.

Pegatron fell 1 percent to close at NT$31.30 in Taipei trading, compared with a 0.4 percent gain in the city’s benchmark Taiex Index.