Voters who had been lining up in front of polling stations half an hour before they opened were seen checking their names on electoral rolls, casting their ballots, and having their fingers inked by electoral workers.
Polls were scheduled to close at 6:00pm (0000 GMT Monday).
Voter intention surveys credited Ortega -- a former Marxist rebel who has ruled since 2007, with a previous stint between 1985 and 1990 -- with an insurmountable lead over his nearest rivals.
His wife, Rosario Murillo, who has long had a leading role as the public face of his government as chief spokesperson, is poised to take charge as vice president if the vote is to confirmed to go their way.
Some in the opposition, which has been sidelined and weakened, have urged voters not to take part in the elections.
