Afghanistan's Independent Election Commission said initial results based on 10 percent of the vote from 26 out of 34 provinces showed former opposition leader Abdullah Abdullah in the lead with 41.9 percent.
Four voters were wounded in an explosion at a polling station in the southeastern province of Logar.
"The blast took place close to a polling station which is a school building and wounded four voters, one critically," Abdul Hameed, governor of the province's Mohammad Agha district, told Reuters.
It was the most serious attack so far on an election that Taliban insurgents had vowed to derail, branding it a 'US backed sham'.
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.