The incident began on Saturday in the suburban My Duc district when authorities clashed with villagers who alleged their land was illegally seized for sale by a military-owned telecoms firm.
The exact number of policemen and officials being held by residents could not immediately be confirmed, but images on social media showed at least 12 uniformed men under guard.
"Local residents said they have no intention of releasing the hostages unless the central government intervenes," said La Viet Dung, a social activist who visited the site Sunday morning.
A My Duc resident told AFP today police had fired in the air during yesterday's clashes.
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"Some residents were also taken into custody by police for unknown reasons," he said, requesting anonymity.
Local police and authorities refused to comment.
But state media said four residents were taken into custody while some police were also being held by villagers.
"Some citizens... Have committed acts of obstruction and illegally held Hanoi police officers," the Vietnam News Agency said, quoting a police announcement.
The government strictly controls freedom of expression and the right to protest but flashpoints occur.
In 2012 a Vietnamese fish farmer used homemade weapons to resist a forced eviction and injured seven policemen.
The farmer was jailed for five years, but his case became a symbol of growing public dissatisfaction over land rights.
In 2013 a gunman killed a provincial official before committing suicide in an apparent dispute over land in northern Vietnam.