The opposition has also claimed a lead, increasing tensions and fears of unrest when full results become known in coming days.
Ballot counting began after polls closed on Wednesday. On Thursday the electoral commission said that with about 86% of the votes counted, the MPLA was ahead with a 52% majority, while its main opposition rivals the National Union for the Total Independence of Angola (Unita), led by Adalberto Costa Júnior, had 42%.
The vote for Unita would be a big advance on previous elections but still below levels needed to threaten the MPLA, in power since Angola declared independence from Portugal in 1975.
Polls before the election had showed the MPLA only seven percentage points ahead but with very large numbers yet to make a choice.
Results in past elections have been contested, in a process that could take weeks.
Observers have warned that discontent with the rule of MPLA has reached a point where the party could only now secure another five years in power through widespread rigging and repression.
An activist monitoring group, Mudei Movement, has taken pictures of results sheets at as many polling stations as possible, fearing the fraud that marred past polls.
Unita urged voters to stay near polling stations after casting their ballots, a call many seemed to be heeding as polls closed on Wednesday evening. “The police said to vote and go home. I told them I would vote and sit down,” said Severano Manuel, 28, in Cacuano, outside Luanda.
The electoral commission earlier said polling had gone smoothly.
Analysts say the opposition will face a dilemma if they reject official results. To instigate a campaign of street protests would leave Unita open to accusations of deliberately fomenting disorder, but to seek redress through legal or other constitutional channels is unlikely to succeed.