Singapore's horse-racing community is in shock over the murder of former Kranji-based apprentice jockey Chung Wah Thong in Penang, The Straits Times reported Thursday.

The report said Malaysian Chung, who was 28, rode briefly at the Singapore Turf Club earlier this year.

The news portal said the STC had Wednesday expressed its deepest condolences to the bereaved family.

Chung, who won 30 races including the Malaysian Group 1 Selangor Gold Cup last year, had relocated to Singapore in January and was indentured to Singaporean trainer Leslie Khoo, said the report.

"It's so senseless and to lose his son and his mother ... makes it even more senseless. WT (Wah Thong) was a quiet boy but he worked hard at the stables," Khoo was quoted as saying.

Besides Chung, three of his family members were also shot dead at a chicken processing factory in Batu Maung, Penang, early Wednesday.

The victims have been identified as Tan Hock Choon, 50, his common law wife Tan Saw Sim, 55, and Chung's two-year-old son named Ah Bee.

Penang CID Chief Datuk Razaruddin Hussain had said based on initial investigations, the act was committed by a close relative.