Embalo was seeking to become the first president in three decades to win a second consecutive term in Guinea-Bissau, a small coastal nation between Senegal and Guinea.
He could not immediately be reached.
A spokesperson for Embalo, Antonio Yaya Seidy, told Reuters that unidentified gunmen attacked the election commission to prevent an announcement of the vote results.
He said the men were affiliated with Dias, without providing evidence. A spokesperson for Dias did not immediately respond to a request for comment.
Former Prime Minister Domingos Simoes Pereira, who lost to Embalo in a contested runoff in 2019 and has backed Dias in this election, said Dias had nothing to do with the incident.
Dias was meeting election observers when “some people erupted in the room to announce that there were gunshots in the centre of the town,” said Pereira, who said he was in the same meeting.
Dias was safe and in Bissau, Pereira said.
Guinea-Bissau had been shaken by at least nine coups and attempted coups between 1974, when it gained independence from Portugal, and 2020, when Embalo took office.
Embalo has said he has survived three coup attempts during his time in office. His critics have accused him of manufacturing crises as an excuse for crackdowns.