Zimbabwe's re-elected President Emmerson Mnangagwa suggested on Sunday that anyone questioning the results of last week's election take their case to court as an opposition leader accused him of "gigantic fraud".

Mnangagwa, 80, won the election with 52.6% of the vote while the opposition Citizens' Coalition for Change (CCC) leader Nelson Chamisa got 44%, the election commission said on Saturday.

Chamisa said on Sunday the CCC would not accept the results.

He said the opposition would form the new government, without giving details. He did not answer questions on whether his party would challenge the results in court.

“We will not wait for five years. There has to be a change now,” Chamisa told journalists and party officials.

Two observers' groups said police raided their data centres and arrested staff and volunteers so they could not independently verify the results.

The Election Resource Centre and the Zimbabwe Election Support Network said in a statement that this “cast a shadow over the entire election process". The police were not immediately available for comment.

Observers from regional body SADC and from the African Union also criticised the election process.

Analysts and observers said the contest was heavily skewed in favour of the ZANU-PF ruling party, which has been in power for more than four decades. ZANU-PF denies it has an unfair advantage or seeks to influence the outcome of elections through rigging.

Chamisa, speaking on social media platform X, formerly Twitter, said of the election: "It's a blatant and gigantic fraud."

He indicated he was counting on diplomatic pressure on the government.

"Do not leave us, particularly our fellow brothers and sisters in the region and on the continent,” he said. “We count on your solidarity as we seek to resolve this political crisis.”

Mnangagwa first became president when longtime strongman Robert Mugabe was toppled in a 2017 military coup after 37 years in power. Mnangagwa's first term was marked by runaway inflation, currency shortages and sky-high unemployment.

Mnangagwa welcomed the result.

"I competed with them and I am happy that I have won the race," he said at State House on Sunday amid heavy police presence in parts of the capital.

"Those who feel the race was not run properly should know where to go to."

This is Mnangagwa’s second and possibly last term as the constitution limits presidential terms to two.

ZANU-PF spokesperson Christopher Mutswangwa said the party, which mustered 136 of 209 seats in the parliamentary elections, was shy of a two-thirds majority.

“We will concentrate more on governance than probably trying to amend the constitution,” he told journalists on Sunday.

Term limits are a contentious issue in the southern African country given the length of Mugabe's rule.