Eighteen Muslim Brotherhood members have been arrested after gunmen opened fire near a polling station in Giza’s Manshatit Al-Kanatir district, a security official told Al-Ahram Arabic news website.
Four people were reportedly injured in the violence near Imbaba on Tuesday afternoon.
Hundreds of Brotherhood supporters had earlier gathered in front of the polling station and set fire to tires.
Security forces used teargas to disperse them.
Four people were killed during separate clashes in Giza on Tuesday.
All Brotherhood attempts to disrupt the referendum have been brought under control, Interior Minister Mohamed Ibrahim told the privately owned Al-Hayat TV channel.
The turnout on the first day of voting was high, he added.
Ibrahim said he had increased the number of police on the streets to deal with attempts to disrupt the poll.
Security forces will remain in place over night to guard polling stations.
Voting will resume on Wednesday at 9am for the final day of the constitution referendum.
At least 9 people were killed on Tuesday in nationwide clashes between Muslim Brotherhood members, local residents and security forces.
The constitution is the first electoral test in the roadmap put in place by the transitional authorities after Mohamed Morsi was ousted in July 2013.
According to the post-30 June political roadmap, a successful referendum will be followed by parliamentary and presidential elections within six months.
Source : Ahram