Zimbabwe's incoming president Emmerson Mnangagwa has assured outgoing leader Robert Mugabe and his family "maximum security" ahead of his swearing in on Friday, state media reported.

"Mnangagwa (Thursday) spoke to (the) outgoing President... and assured him and his family maximum security and welfare as he appraised him of preparations for (Friday's) inauguration," the state-run Herald news site reported, adding it was unlikely Mugabe would attend as he "needed time to rest".