President Xi Jinping and Premier Li Keqiang sent condolence messages on Sunday to their Sri Lankan counterparts after multiple deadly attacks shook the country.

Xi, in his message to Sri Lankan President Maithripala Sirisena, said he was shocked to learn of the series of explosions in Sri Lanka, which have caused large casualties, Xinhua News Agency reported.

"I, on behalf of the Chinese government and people, as well as myself, send deep condolences to the victims, and my sincere sympathy to the injured and families of the victims," he added.

The Chinese government and people will firmly stand by the people of Sri Lanka and firmly support the Sri Lankan government's effort to maintain national security and stability, Xi said.

Li sent condolences to Sri Lan-kan Prime Minister Ranil Wickremesinghe over the attacks.

Multiple explosions hit the South Asian country on Sunday, claiming at least 290 lives while over 500 have been injured, officials said.

Sri Lankan Health Minister Rajitha Senaratne said at a news conference on Monday that a group named National Thowfeed Jamaath is responsible for the bombings, while foreign links are also suspected. The National Thowfeed Jamaath is a local militant radical Islamist group in Sri Lanka, officials said.

Reuters said Sirisena will ask for foreign assistance to track international links to the series of attacks. He declared a nationwide emergency would go into effect at midnight on Monday.

The Sri Lankan government imposed a new dusk-to-dawn national curfew, from 8 pm Monday to 4 am local time on Tuesday, according to local police.

Agence France-Presse said 35 foreigners were killed in the blasts, including Chinese, British, US, Turkish, Indian, Danish, Dutch and Portuguese nationals while Sri Lankans accounted for most of the dead and wounded.

Xinhua News Agency reported Monday night that one Chinese citizen was killed, five were missing and five injured, citing an update from the Chinese embassy.

Foreign Ministry spokesman Geng Shuang confirmed on Monday that Chinese citizens were dead or missing after the explosions. The five Chinese who were injured were in stable condition, he said.

The ministry and the Chinese embassy in Sri Lanka initiated an emergency response plan immediately after the explosions to check on Chinese casualties and locate the missing, and they will continue to follow developments closely, Geng said.

Long Xingchun, director of the Center for Indian Studies of China West Normal University, said such an attack has rarely been seen in Sri Lanka's history "in terms of its skill, intensity and ferocity". He said it is possible that dispersed Islamic State or al-Qaida extremists could have fled to Sri Lanka to carry out attacks in cooperation with local extremists.

Long said that because tourism is an important sector of Sri Lanka's economy, the attacks, which coincided with the Easter holiday and targeting high-end hotels, will undoubtedly hurt the tourism industry and economic development in Sri Lanka.