MANILA — President Obama turned up the heat again on China’s growing assertiveness in the South China Sea on Wednesday as world leaders gathered here for the start of the Asia-Pacific Economic Cooperation (APEC) summit meeting.

Speaking to reporters after a meeting with Philippine President Benigno Aquino III, Obama said they discussed how to address China’s provocations in disputed areas of the sea, including its creation of new islands and construction of lighthouses, ports, military facilities and airstrips.

“We agree on the need for bold steps to lower tensions, including pledging to halt further reclamation, new construction, and militarization of disputed areas in the South China Sea,” Obama said.

The South China Sea dispute has been a major focus surrounding the APEC event, which brings together 21 Pacific Rim leaders to focus on trade and business issues in the region. Countries such as the Philippines worry about China’s military presence and its domination over fishing grounds that have long been used by many nations in the region.

The president’s statement came on the heels of Tuesday’s visit to a Philippine Navy vessel and his announcement that the U.S. would transfer two additional ships to the Philippine Navy and provide $250 million in maritime security assistance to allies and partners in the region.

Once the APEC summit got underway, however, Obama toned down his rhetoric, focusing his remarks before an audience of business leaders almost entirely on the issue of climate change.

“If we want to prevent the worst effects of climate change before it’s too late, the time to act is now,” the president said, looking ahead to the upcoming global climate change conference in Paris at the end of November.

He underscored to his audience that clean energy offers great potential for future growth. “An ambitious agreement in Paris will prompt investors to invest in clean energy technologies because they will understand that the world is committed to a low-carbon future,” he said. “That’s a signal to the private sector to go all-in on renewable energy technologies. If we can get an agreement done, it could drive new jobs and new opportunities, an investment in a global economy that frankly needs a boost right now.”

Directly following Obama, Chinese President Xi Jinping addressed the CEO meeting. He also avoided the sensitive South China Sea issue, and instead delivered a policy platform highlighting China’s growing economic clout in the region as it becomes an economic counterweight to the United States.

Nor did Xi  mention the U.S.-led Trans-Pacific Partnership (TPP) trade agreement by name, but he cited “various new regional free trade arrangements popping up,” and warned that “there have been worries about the potential of fragmentation in this regard.” The 12-nation pact excludes China.

Xi instead promoted China’s ambitious “One Road, One Belt” economic integration initiative and the new China-led Asian Infrastructure Investment Bank, which will challenge the World Bank and other international financial institutions in financing regional infrastructure projects. The Obama administration opposes that venture, fearing Chinese economic domination in Asia.

Although the APEC summit is focusing on economic issues, the South China Sea dispute continued to lurk in the background.

“The Chinese have said they felt the APEC forum was not an appropriate forum to discuss the South China Sea,” said Curtis S. Chin, former U.S. Ambassador to the Asian Development Bank and currently Asia Fellow at the Milken Institute. “I argue to the contrary, that the economic and the political cannot be separated. At the heart of trade and economic growth is freedom of navigation. How do you have trade when you can’t sail through waters a few miles off your coast? I felt today was a missed opportunity for President Obama in a very diplomatic way to make these points.”

After the CEO Summit, Obama participated in a meeting on the Trans-Pacific Partnership with the heads of state of the pact’s other 11 member countries. He also met separately with other leaders in attendance.

Chin said that talks on the sidelines of the summit may be the most productive ways to advance issues such as the TPP and the peaceful resolution of South China Sea territorial disputes, on which China has shown very little willingness to concede anything.

“[Peaceful resolution] will likely mean give and take on all sides, but clearly there’s been very little give on the Chinese side,” he said. “When it comes to these South China Sea territorial disputes, it’s all take.”