President Xi Jinping sent a message of condolence to his Sri Lankan counterpart Maithripala Sirisena on Sunday after flooding and a landslide left more than 150 people dead.
Xi expressed deep sorrow for the people who lost their lives and extended his sympathy to those affected by the disaster as well as the family members of those killed.
He also highlighted the friendly relationship between the countries and offered all-out support to the Sri Lankan government and help with the disaster relief effort.
Xi said he was confident the Sri Lankan government and the people will overcome the disaster and rebuild their country.
Premier Li Keqiang also sent a message of condolence to Sri Lankan Prime Minister Ranil Wickremesinghe on Sunday.
The message of support came as emergency teams rushed to distribute aid to half a million people who have been displaced by the flooding, as authorities upgraded the death toll to 151.
The official Disaster Management Centre said 111 people were still missing, with 95 injured in hospital, since torrential rain and landslides swept away entire villages.
Floodwaters were receding in some areas after a break in the rain, giving authorities a chance to deliver much-needed supplies to victims who lost everything in the deluge.
Heavy rains on Friday triggered the worst flooding and landslides in 14 years in the southern and western parts of the island.
Many villages were still underwater on Sunday, officials said.
Nearly 2,000 houses were damaged or completely destroyed. Almost half a million Sri Lankans had been forced from their homes, with most moving into temporary shelters.
The charity Save the Children said about a tenth of those displaced were children below the age of five years.
It said that the stagnant floodwaters provide the perfect breeding ground for mosquitoes and could exacerbate the dengue crisis that has seen an almost 150 percent increase in cases compared to the same period last year.
"The humanitarian situation in Sri Lanka right now is alarming. The impact of these early monsoon season downpours has been far more devastating than what we'd normally expect this time of the year," Save the Children's Chris McIvor said.
Medical teams have been dispatched to the worst-affected areas to help prevent an outbreak of waterborne diseases.
"We have the expertise to deal with this situation," Health Minister Rajitha Senaratne said, adding that cholera and diarrhea had been successfully prevented in past floods.
The government, meanwhile, has withdrawn an evacuation order for thousands of residents in the southern district of Matara as water levels subsided.
The United Nations said it will provide water containers, water purification tablets and tarpaulin sheets while the World Health Organization will support medical teams in affected areas.
