Tonga Police said a rescue mission was underway to find the missing diver.
Police received report of the incident involving the two men from Pātangata at 11.30pm on Tuesday, a report on Tonga Police official Facebook page said.
Kaniva News reports Police have yet to release the detail of the incident.
It comes after the government announced last month it has lifted the ban on sea cucumber fishing, citing request from the fishing community to allow it to help alleviate the negative financial impacts of the Covid-19 crisis.
