Zimbabwe’s opposition leader, Nelson Chamisa, has claimed he is “winning resoundingly”, as counting of votes in the country’s election continued.

Millions of people voted peacefully on Monday in the first poll since the army removed Robert Mugabe from power last year. Long queues of voters formed outside polling stations, and the Zimbabwe Election Commission (ZEC) said 75% of the 5.6 million registered voters had cast their ballots. Observers said they had seen few problems other than some poor organisation in places.

The election pitted Chamisa, 40, a lawyer and pastor whose only experience of power was a stint as a minister in a coalition government several years ago, against Emmerson Mnangagwa, 75, a longtime Mugabe aide and head of the ruling Zanu-PF party. The two represent dramatically different ideologies and political styles, as well as generations.

Chamisa said in a 5am tweet that the Movement for Democratic Change had “done exceedingly well”, according to results from a majority of polling stations.

There was no confirmation of his claim and the official count will not be announced for several days. However, results from each of 10,985 polling stations are posted in public by officials. Several civil society groups are collating these, though they are not allowed to release full results before the official tally is known.

Activists said the results were still too close to call but the general trend appeared to be in the opposition’s favour. Mnangagwa tweeted that he was “delighted by the high turnout and citizen engagement so far”.