An AFP correspondent saw plainclothes police drag around 20 people away and move them to nearby buses. Authorities could not be reached for comment.
The protest went ahead despite a concession by the communist government, which said yesterday that it would ask parliament to delay approving the law until the end of the year.
Prime Minister Nguyen Xuan Phuc also told local media on Thursday that the government would seek to reduce the period of the leases, but did not say by how much.
Today's demonstration followed the arrest of two people the previous day in the southern province of Binh Duong for spreading leaflets calling for protests against the legislation, state media reported.
Images on social media showed demonstrations in Ho Chi Minh City and other parts of Vietnam, as calls for action spread on Facebook earlier last week.
A state media outlet also reported that protesters in Binh Thuan province on the south-central coast had blocked traffic and thrown rocks at police.
Public shows of dissent are rare in the one-party state, where a conservative leadership in place since 2016 has taken a more aggressive stance against activists.
A Vietnamese environmental activist was jailed for 14 years in February over protests against a toxic waste dump that killed tonnes of fish in 2016, an incident that sparked nationwide demonstrations.
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