China has called off some planned exchanges with Vietnam and dispatched aircraft and ships to pick up injured and frightened Chinese nationals caught in violent anti-China riots.
Since Tuesday, severe riots have erupted in many places in Vietnam, leading to robbery, arson and vandalism against foreign businesses, and to casualties and property damage of Chinese citizens, Foreign Ministry spokesman Hong Lei said.
"The violence has sabotaged the atmosphere and conditions for communication and cooperation between China and Vietnam," Hong said, adding that Beijing will take further action as the situation develops.
When China started drilling for oil around its Zhongjian Island in the Xisha Islands in early May, Vietnam, which claims the waters belong to it, sent military and civilian ships to interrupt the Chinese operation.
The protests in Vietnam turned into violent attacks on companies from the Chinese mainland, Taiwan, Japan, South Korea and Singapore.
Two Chinese were killed and hundreds were injured by rioters in the past week.
Vietnamese authorities arrested more than 1,000 rioters following international attention.
On Sunday, the protests did not become as large as protesters had planned.
The Associated Press reported that Vietnamese authorities beefed up security on Sunday in two major cities to clamp down on protests against China.
In southern Ho Chi Minh City, police dragged away several demonstrators from a park in the city centre. In Hanoi, authorities closed off streets and a park close to the Chinese embassy and pushed journalists and protesters away, AP quoted local activists as saying.
Xu Liping, a Southeast Asian studies researcher at the Chinese Academy of Social Sciences, said the Vietnamese protests, aimed at flexing muscle against China over its maritime claims, have gone far beyond law and morality.
"In return, China's decision to cancel part of its exchange plans, on one hand, shows Beijing's firm will to safeguard sovereignty and protect Chinese nationals, and on the other hand opens channels for communication," Xu said.
Wu Shicun, president of the National Institute for South China Sea Studies, said the harassment against Chinese oil operations and the violence against foreign businesses has damaged trust between the two countries.
"Vietnam has to restore social order and guarantee the personal safety of Chinese nationals as soon as possible before it further wrecks bilateral relations and its own social stability," Wu said.
"The investment environment will deteriorate as long as violence continues. Foreign capital will withdraw and the Vietnamese economy will suffer a bad recession," he said.
On Sunday, China dispatched five ships to Vietnam to evacuate Chinese, the Ministry of Transport said.
The Hainan Maritime Safety Administration said a rescue vessel has been sent to provide emergency support. Another rescue vessel and a rescue helicopter are on standby.
Qi Xiaofeng, a spokesman for the Chinese embassy in Vietnam, said 135 Chinese workers injured in the riots in Vietnam's central Ha Tinh Province were flown home.
More than 3,000 Chinese nationals had been evacuated from Vietnam as of Saturday afternoon with the assistance of the Chinese embassy, the Foreign Ministry said on Sunday.
Xinhua contributed to this story.