The protests were in response to Beijing's unilateral move to develop islands in the South China Sea claimed by both nations.

Crowds gathered near the Chinese Consulate here yesterday, chanting patriotic slogans, waving Vietnamese flags and shouting anti-Chinese slogans.

It was a repeat of similar noisy demonstrations here and in Hanoi the weekend before.

Such public protests are almost unheard of in Vietnam where security forces maintain strict control and crack down quickly on any political gatherings of any sort.

But yesterday, the police again allowed the demonstration to go ahead, although security was beefed up around the Chinese Consulate, with its sidewalks sealed off. The protesters then moved to a nearby park opposite Notre Dame Cathedral in downtown Ho Chi Minh City.

The mostly student protesters were also thwarted by massive security from marching onto the Chinese Embassy in Hanoi. Instead, they marched through the centre of the capital, shouting anti-Chinese slogans and singing patriotic songs.

Most of the demonstrators wore identical T-shirts with the red- and-gold Vietnamese flag, a map of Vietnam that includes the disputed islands, and the words 'China hegemony jeopardises Asia' and 'Beware of the invasion'.

The row over the disputed islands, which are reportedly rich in oil and gas deposits, threatens to cause a further deterioration in the already tense Sino-Vietnamese relationship.

Both nations claim the disputed Spratly and Paracel islands in the South China Sea (which Vietnam calls the East Sea).

After last week's protests, Beijing sharply criticised its southern neighbour.

Chinese Foreign Ministry spokesman Qin Gang said: 'China has indisputable sovereignty over the South China Sea islands.'

He specifically chided Hanoi for allowing and possibly encouraging the protests.

'Recently in Vietnam, there have been developments unfavourable to friendly ties between China and Vietnam, and we are highly concerned,' said Mr Qin.

He urged the Vietnamese leaders to 'prevent further developments and avoid harming bilateral relations'.

But it appears that Hanoi is not in the mood to back off.

There is particular annoyance at the way Beijing has warned international oil companies that if they participate in Vietnamese exploration projects in the disputed waters they will be excluded from the Chinese market.

After receiving such a warning in June this year, BP (British Petroleum), and its partners US oil giant ConocoPhillips and state-owned Petrovietnam, halted a US$2 billion (S$3 billion) project to develop a gas field off south Vietnam.

Diplomatic sources say the BP precedent has caused other projects to be sidelined.

The cancellation of these oil developments has infuriated energy-hungry Vietnam and led to the government tacitly condoning anti-Chinese sentiment.