Hundreds of people have been arrested in a government crackdown after deadly riots targeting Chinese people in Vietnam, senior Vietnamese officials said Thursday, warning anyone found in breach of the law would face tough punishment.

"The Vietnamese government has... contained the acts of law infringement and (will) strictly punish violators in accordance with the law," Prime Minister Nguyen Tan Dung said in a speech to an economic conference in Manila.

"As a result, the situation has become totally stable. The enterprises' business and production have come back to normal," Dung added.

Vietnam's Deputy Foreign Minister Pham Quang Vinh later told reporters "hundreds of people" were in "temporary detention" in connection with the riots, which targeted Chinese and other foreign-owned businesses last week.

"They will be seriously punished in accordance with the law, including bringing them to justice in court," Vinh said.

Dung said the Vietnamese were protesting at what he alleged was China's illegal deployment of a deep-sea oil rig in South China Sea waters also claimed by Hanoi.

The Chinese foreign ministry said Wednesday that four people were killed and more than 100 others injured in last week's violence.

Thousands of Chinese have returned from Vietnam since the protests, according to official media reports in Beijing.

Hanoi initially lauded "patriotic" displays by its citizens, but backpedalled furiously after the violence badly stained the country's image as a safe destination for sorely needed foreign investment.

"The entire Vietnamese nation has been protesting against China's wrongdoings. In various localities of the country, the people have spontaneously launched demonstrations, in which some people became restive and violated the law," Dung said Thursday.

China claims almost all of the South China Sea, parts of which are also claimed by the Philippines, Brunei, Malaysia and Vietnam, all members of the Association of South-East Asian Nations (ASEAN), and non-member Taiwan.

Last week leaders of the 10-nation bloc presented a rare united front by expressing "serious concern" over disputes in the waters, which are home to key shipping lanes and thought to contain vast energy reserves.

The United States, allied to Vietnam and the Philippines, has refused to take sides while warning about the potential for tensions to escalate.

Dozens of Chinese and Vietnamese vessels have engaged in repeated skirmishes near the rig, including reported rammings and the use of water cannon.