RAIDS by police are not uncommon in Vietnam but visits to bookshops to confiscate issues of travel guide Lonely Planet are unusual.
The guidebook has raised the ire of authorities because its maps mention the South China Sea, which in Vietnam is firmly referred to as the East Sea (China calls it the South Sea).
The vast oil, gas and fish-rich area and the Spratly and Paracel islands are contested by Vietnam and China. The Philippines, Taiwan, Brunei and Malaysia also lay partial claim to the area.
Tensions between Vietnam and China rose again recently when China's National Offshore Oil and Gas Corporation invited foreign companies to bid on blocks Vietnam says are part of its Exclusive Economic Zone. Foreign companies already operate there, under the protection of Vietnamese patrols.
A bookshop owner who had been visited by the Ministry of Information said things were ''more sensitive now because of the tension with Vietnam and China''. They have also put away other books likely to anger authorities as more general crackdowns are common in times of tension (bars will often be closed early by police in Hanoi for the same reasons).
Anti-China sentiment in Vietnam is sometimes tacitly encouraged as a way to ''send a message to Beijing'', but it is also closely monitored lest it spill over into anti-government sentiment. Bloggers have been arrested in the past for criticism of their government's dealings or supposed capitulation to China.
These past two weeks anti-China protests have been held in Hanoi, albeit under the watchful eyes of police. From April last year there were nearly a dozen protests, held every Sunday morning in the centre of the city. After a rapprochement with Beijing they were swiftly shut down. That last round was sparked by the cutting of cables of a Vietnamese survey ship, supposedly by a Chinese naval vessel. The detention of Vietnamese fishermen has also raised ire.
During the ASEAN Summit in Phnom Penh, Cambodia, last week US Secretary of State Hillary Clinton said: ''We do have an interest in freedom of navigation, the maintenance of peace and stability, respect for international law and unimpeded lawful commerce in the South China Sea,'' despite the US having no territorial claims in the vast waters. Mrs Clinton had visited Hanoi the day before.