Demonstrators clashed with police in Vietnam in protests against plans for new economic zones that some fear will be dominated by Chinese investors.
Police reportedly detained more than a dozen people in the capital Hanoi and halted demonstrations in other cities.
Some carried anti-China banners, including one reading: “No leasing land to China even for one day.”
The government proposed a law last year that would give foreign investors a 99-year lease on Vietnamese land.
The bill offers them greater incentives and fewer restrictions, in an attempt to promote growth in target areas.
The protesters suspect that the communist government will award Chinese investors leases in the three economic zones in the north-east, south-east and south-west of the country, and that this would be a pretext for Chinese control over the island of Van Don near their shared border.
China once colonised Vietnam, the two countries fought a border war less than 40 years ago, and Vietnam contests Chinese control of a number of islands in the South China Sea.
As a result, says BBC South East Asia correspondent Jonathan Head, Vietnam’s leaders must always tread a delicate line between maintaining relations with their powerful neighbour, and avoiding provoking anti-Chinese sentiment in a fiercely nationalist population.