President Robert Mugabe vowed on Saturday that the opposition Movement for Democratic Change would never rule Zimbabwe, adding he was prepared to fight.
At least 12 members of the party, including opposition leader Morgan Tsvangirai, were also arrested, the MDC said.
"We shall never, never accept anything that smells of a delivered parcel of what they call the MDC ... that is not going to happen. We are prepared to fight for it if we lose it in the same way that our forefathers lost it," Mugabe said referring to British colonial rule.
Tsvangirai and 11 other members of his party were being held at a police station, the MDC said.
In a statement, the party said Tsvangirai was arrested at a road block with his campaign team. He has been detained several times over the past week.
Tsvangirai, rights groups and Western powers accuse Mugabe of unleashing a brutal campaign, including using police to harass opponents, to win a presidential run-off vote scheduled for June 27.
Mugabe and his ZANU-PF lost presidential and parliamentary elections on March 29.
A second ballot, however, is required because Tsvangirai fell short of the majority needed to win the presidency outright. He says 66 of his followers have been killed since the March poll.
Meanwhile, police on Saturday brought the Zimbabwe opposition's second-in-command to court.
Reporters watched as Tendai Biti, handcuffed and appearing tense, was brought into Justice Ben Hlatshwayo's court.
Biti, secretary-general of the MDC, was arrested upon returning to Zimbabwe from neighboring South Africa on Thursday.
Police say he faces a treason charge, which can carry the death penalty.