Mr Schumer was in China co-leading a bipartisan Congress delegation when the Palestinian militant group fired over 3,000 missiles at Israel on Saturday, prompting prime minister Benjamin Netanyahu to declare his country was at "war".
Israel retaliated by bombarding over 1,000 alleged Hamas and Islamic Jihad targets in the Gaza Strip, that killed more than 400 people. On the Israeli side, at least 700 people have been reportedly killed, while thousands have sustained injuries.
Palestinian militant groups claimed to be holding over 130 Israeli civilians and soldiers captive in Gaza.
"I was very disappointed, to be honest, by the foreign ministry’s statement that showed no sympathy or support for Israel during these tough, troubled times,” Mr Schumer said during a meeting with top Chinese diplomat Wang Yi on Monday.
"The ongoing events in Israel over the past few days are horrific," he said.
Mr Schumer urged the Chinese diplomat and "Chinese people to stand with the Israeli people and condemn these cowardly and vicious attacks".
A Chinese foreign ministry statement on Sunday urged both sides to exercise restraint and immediately end hostilities to protect civilians, without mentioning Hamas.
China suggests that "the fundamental way out of the conflict lies in implementing the two-state solution and establishing an independent State of Palestine".
Beijing has traditionally backed the Palestinian cause but has also boosted ties with Israel as it seeks a larger role in trade, technology, and diplomacy.
President Joe Biden has moved ships and warplanes closer to Israel as he vowed to provide "rock solid" support to the country.
He spoke to Mr Netanyahu and "conveyed that additional assistance for the Israeli Defence Forces is now on its way to Israel with more to follow over the coming days," the White House said in a statement.
The bipartisan congressional delegation to Asia, which includes stops in South Korea and Japan, aims to advance US economic and national security interests. The delegation hopes to meet Chinese president Xi Jinping.
Mr Wang said China hoped that this visit can help the US understand China in a more precise and objective manner while managing existing contradictions more reasonably.
Mr Schumer reiterated that the main objective of the trip was to seek economic reciprocity and the creation of a level playing field for US businesses in China, and assured that Washington was not seeking conflict with Beijing.
“China must also provide a level playing field for American companies and workers. Many Americans, most Americans, including our delegation, do not believe we have that fairness now,” he added.
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