South Africa will send anti-piracy patrols to the waters off Mozambique and Tanzania this month, a senior navy official said on Thursday, while warning of a resurgence in attacks if the continent's oceans are not policed.

"Piracy is not over," said Rear Admiral Bernhard Teuteberg, director of maritime strategy for the South African Navy on the side-lines of a conference on African maritime security.

Piracy attacks off the coast of Somalia have plummeted to a three-year low thanks to beefed up naval patrols, but Teuteberg said that a withdrawal of patrols would allow ship hijackings to flare up again.

"I think if those forces would withdraw, we would once again see some increase in piracy."

To protect trade as sea conditions improve with the arrival of the southern hemisphere's summer, South Africa is moving assets to the coast of Mozambique and Tanzania.

"We intend towards the end of November once again to put certain forces and assets within the northern Mozambican channel and off the coast of Tanzania," he said.

"We can never give up, we can never leave the northern Mozambique channel. We can never leave the area off Somalia because if we leave a vacuum, piracy will return," he said.

Last month, the International Maritime Bureau said piracy and armed robbery at sea were down globally to 233 incidents so far this year, the lowest third-quarter total since 2008.

Attacks by Somali pirates had also fallen to its lowest level since 2009, with only 70 attacks in the first nine months of the year, compared with 199 in 2011.

International navies and boosting security onboard ships were cited as key deterrents.