Waikato Hospital is resourced to employ four full-time equivalent positions but it only has 2.3.
The DHB wouldn't say if any of the doctors also worked in private practice. The department currently has an interim clinical director.
A source told the Herald the service was so understaffed that it may not be able to provide patients with major facial trauma expert care without calling in outside help.
A Waikato DHB spokesman denied patient safety was at risk and said when more on-call cover was needed locums or neighbouring DHBs would be called in.
"Each SMO [senior medical officer] is required as part of their employment contract to participate in the on-call roster," he said.
"In the event of a vacancy, discussions are held with SMOs within the department to determine availability to provide cover.
"Where additional cover is required an external solution is sought by way of locum or broader network cover."
The DHB said the effects of the Covid-19 pandemic and the vacancies meant the wait for non-urgent surgeries had increased from four months to seven.
It meant elective surgeries had reduced by two to three patients a week.
"Patients are prioritised in order of urgency and time waiting. There is a plan to outsource some to private facilities."
The Covid-19 lockdown temporarily halted non-urgent surgeries across the country causing the backlog at the department.
The DHB said it was actively recruiting to fill the vacant roles but because of Covid-19 international candidates had become increasingly difficult to recruit.
"But an offer has been made along with a number of discussions under way to bring suitably qualified candidates onto the team."
The offer of employment had been accepted and the person would start in January.
"We are still recruiting to the second position."
In 2018 the hospital's plastic surgery department was so severely understaffed doctors said they were constantly on call and working days without rest, putting patients at risk and forcing cancellation of clinics and surgeries.
The junior doctors claimed the unit was operating illegally because of the shortage and forced the DHB to make changes.