Mugabe's ZANU-PF party posted a disclaimer Thursday saying it awaited the release of results by the state election commission, the only body allowed under the law to announce the outcome of massive voting on Wednesday.
But witnesses said figures displayed outside polling stations in the Mbare township of Harare, a stronghold of Prime Minister Morgan Tsvangirai since polls in 2002, showed Mugabe winning there.
Tsvangirai's party is claiming widespread electoral fraud. Witnesses said it won just four of 26 parliament seats in the eastern Manicaland province it had dominated.
Extra police, some in riot gear, deployed in Harare on Thursday.