They fear that new groups will join the conflict after Eid al-Fitr.
The Maute Group and other rebels are targeting Christians in the fight to takeover the city.
There are fears the war across the border in the Philippines will kickstart a flood of militants across the border.
China's relationship with South China Sea neighbors is often contentious.
The war has lasted for 14 days in the southern island of Mindanao.
"I can end this war in 24 hours. All I have to do is to bomb the whole place," Philippines President Rodrigo Duterte said.
The attack by Islamist militants on Marawi had "all the hallmarks of a professional military operation."
ISIS claimed responsibility for the shooting via its Amaq news agency.
Philippine authorities say there's no evidence of terrorism in the attack which left 36 dead and dozens wounded.
Earlier, President Donald Trump said Washington was closely monitoring what he described as a "terrorist" attack unfolding in Manila.
Dozens of people are reported injured after an attack at a resort in Manila.
"It's very sad to be hitting our own troops," Defense Secretary Lorenzana said.
The army has used airstrikes and street combat, yet still the Maute Group Islamist militants fight on.
The army has used airstrikes and street combat to try and force out the Maute group militants who took hold of the city a week ago.
Attached to one of the bodies was a sign that said "Munafik", meaning "traitor."
It was not the first time Duterte has made a joke about rape.
Manila has deployed helicopters and commandoes to retake Murawi from jihadists.
Militants took a local priest and more than a dozen churchgoers and staff hostage.
Malaysia, the Philippines, Vietnam, Japan, and China all claim parts of the South China Sea.
Manila is looking to ease tensions with Asia's top economic power.
"Here's the shocker: I will kill you. I will really kill you. And that's why the rapporteur of the U.N. is here, investigating extrajudicial killing," Duterte said.
The Philippines is currently involved in a maritime dispute with China over its interests in the South China Sea, although Duterte is attempting to forge closer ties with the country.
The notoriously blunt Duterte said the Southeast Asia region was extremely worried about tensions between the United States and North Korea, and said one misstep would be a "catastrophe."