Far-left candidate Pedro Castillo leads the Peruvian presidential race among 18 candidates with 16.1 per cent of the vote, according to an Ipsos exit poll.
Conservative Keiko Fujimori and liberal economist Hernando de Soto are tied in second place with 11.9 per cent.
In fourth place is social conservative Yonhy Lescano, with 11 per cent of the vote, followed by ultra-conservative Rafael Lopez Aliaga with 10.5 per cent and leftist Veronika Mendoza with 8.8 per cent, according to Sunday's the exit poll.
The official results were expected to start coming in late Monday night local time.
The top two candidates will advance to a second round in June.
The poll of 30,000 voters leaving polling stations in 150 provinces had a 3-point margin of error.
The tight race has led to jitters among market watchers of the world's second-largest copper producer and seen the sol currency trade at historically low levels against the dollar.
There were celebrations following the early result indicator in Castillo's home city of Cajamarca, in Peru's northern highlands.
"I am grateful to the Peruvian people for this result," Castillo told supporters, "and I ask for calm until the final results".
Castillo, 51, a primary-school teacher and union leader, put on a late surge in the polls, proposing answers for many of Peru's poorest people, particularly in the country's largely rural interior.
He has promised to redraft Peru's 27-year-old constitution, one of the key demands of young protesters who launched anti-government demonstrations late last year, with a view to weakening the business elite and giving the state a more dominant role in sectors such as mining, oil, hydropower, gas and communications.
Voters were also choosing a new Congress.
Another highly fragmented 130-member legislature is expected.
Peru is engulfed in a second wave of the coronavirus pandemic, on Saturday reporting 384 deaths in a grim new daily record.
Australian Associated Press