Information commissioner Ibim Semenitari said the lock-down, from 7:00 pm (1800 GMT) to 6:00 am was "to prevent the breakdown of law and order because of the tense political situation".
Rivers state in the oil-producing Delta is considered a key battleground for the presidential election, which is seen as the closest in the country's history.
The national main opposition All Progressives Congress (APC) has alleged vote-rigging by the ruling Peoples Democratic Party (PDP) and election officials at the weekend vote.
Armed police and soldiers prevented the women, who were all dressed in black, from entering the offices, forcing them to disperse and reassemble at the government headquarters.
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"What happened today was unprecedented," said APC women leader Victoria Nyeche, a local lawmaker.
"The police teargassed and injured some of us during a peaceful protest at INEC (Independent National Electoral Commission).
"All we want is a fresh election because what happened on Saturday was a fraud."