Thursday’s voting is taking place in nine provinces, with close to 1800 candidates contesting 136 seats.
The opposition Muslim Brotherhood has already secured 76 seats in the first two rounds, five times its tally in the outgoing parliament, and could reach the 100 mark if half of its 49 third-phase candidates win.
The movement's leader, Mohammed Mehdi Akef, said on Wednesday that more than 500 of its supporters had been detained in the run-up to the third phase, mainly in the Nile Delta.
Riot police restricted access to some polling stations in the final stage of Egyptian elections on Thursday in what the Islamist opposition said was an attempt to cap its gains in parliament.
Riot police surrounded a polling station in the Nile Delta town of Kafr al-Sheikh and let only a trickle of voters through their lines to cast ballots.
Riot police prevented voters from
approaching a polling station
The Brotherhood said police had closed four polling stations and detained campaign workers in Kafr al-Sheikh.
Al Jazeera said security forces had detained for half an hour its crew covering the election in Kafr al-Sheikh and destroyed their tape.
Islamist activists were also arrested in Damietta and candidates' delegates were unable to monitor polling, the Brotherhood said.
Run-offs between the top two candidates will be held on 7 December for seats where no candidate wins a clear majority.
The first two phases of the month-long elections which kicked off on 9 November already determined 302 of the People's Assembly's 454 seats.