As Nigerians wait for the final results of the tight presidential election, opposition challenger Muhammadu Buhari has edged ahead of President Goodluck Jonathan by 11.5 million votes to 9.5 million with three quarters of ballots already counted, according to official results collated by Reuters. 

With 60 million registered to vote, turnout in the contest been low, at less than 50 percent.

Party representatives, along with national and international observers and media, were present as the counting of votes began, however the process started two hours later than expected without explanation, according to British newspaper The Guardian.

Early results showed that in eight states and the capital Abuja, incumbent President Jonathan’s People's Democratic Party (PDP) has a lead of about 20,000 votes, according to the BBC.

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Of the nine regions announced, the PDP has taken four, with 2,322,734 votes, while Gen. Buhari's All Progressives Congress (APC) has won five, with 2,302,978 votes.

The final results in the closely contested poll are due Tuesday, according to electoral offcials.

Jonathan’s PDP has been in power since Nigeria returned to civilian rule in 1999, however Buhari has proven to be a strong contender.

This year’s election is reportedly one of the closest in Nigeria's history, and the first with a credible opposition challenge. All eyes now are on the final results.

When are the results going to be announced? I’m literally tired of refreshing my page. #Nigeriadecides #Nigeria2015 #NigeriaElections

— ☠DaMainBoss☠ (@FaYiMoRa) March 29, 2015

The voting process was marred with violence in the northeast of the country, where about 40 people were reportedly killed by the extremist group Boko Haram.

RELATED: Amid Violence and Protests, Nigeria Awaits Election Results

There were also protests over the election process and the alleged manipulation of the vote count process, which has heightened fears of poll-related violence.

International election observers gave broadly positive reactions to the ballot counting process, according to Reuters, despite late delivery of election materials and technical glitches in the new voter authentication devices.

In a joint statement in Switzerland, U.S. Secretary of State John Kerry and British Foreign Secretary Philip Hammond said, "So far, we have seen no evidence of systemic manipulation of the process." They added, however, that there are “disturbing indications” of “deliberate” political interference in the collation process.

The Independent National Electoral Commission (INEC) says there is no basis for this claim. Kayode Idowu, spokesman for the INEC, told AFP "There is no interference at all ... We have no evidence of political interference."

#NigeriaDecides: as #Nigeria tallies election results, concerns mount over vote tampering - http://t.co/Iwv9Vb2EA6 pic.twitter.com/8TlV8TT8Ya

— Voice of America (@VOANews) March 30, 2015