A young apprentice died in a Melbourne factory last month just minutes after a Victorian WorkSafe inspector finished a safety visit at the site.

Dillon Wu is believed to have suffocated while working alone inside a large metal tank at the Marshall Lethlean transport tanker factory in Melbourne's outer east on October 4.

A WorkSafe report from the same day shows an inspector was on site at Marshall Lethlean from 8:00am to 9:45am, and the 20-year-old died at around 10am.