China had previously balked at conducting the inspections, saying they would only increase tensions. But television pictures showed Chinese custom agents searching trucks heading across the border, according to Reuters.
Still, the Chinese customs agency and its commerce and foreign ministries refused to say whether the inspections were due to the U.N. Security Council vote Saturday to impose sanctions, reported the Associated Press.
And Xu Guangyu of the China Arms Control and Disarmament Association, a government-sponsored institute, told Reuters that China does not see the need to impose widespread inspections.
"This is more a symbolic step than a real sanction measure," he said. "China just doesn't engage in that sort of trade with North Korea, so there's not much practical that needs to be done. It lets North Korea know our feelings."
Weapons trade is a tiny fraction of the $1.5 billion trade between the two countries, according to China's customs figures, Reuters reported.
U.S. Undersecretary of State for Political Affairs R. Nicholas Burns has said there will be "enormous pressure on China to live up to their responsibility" in enforcing the sanctions, according to the AP.
On Saturday, the 15-member U.N. Security Council unanimously agreed to impose sanctions on North Korea less than a week after the communist nation said it conducted an underground nuclear test.
The U.N. resolution orders the elimination of all North Korean nuclear weapons, weapons of mass destruction and ballistic missiles.
The measure also provides for a travel ban on officials working on such programs and calls on all countries to inspect cargo leaving and arriving in North Korea to prevent illegal trafficking in unconventional weapons or ballistic missiles.
In addition, the U.S.-drafted resolution calls on North Korea to re-engage in six-nation talks over its nuclear program.
North Korea's U.N. Ambassador Pak Gil Yon walked out after the vote, rejecting the resolution and accusing the council of "gangster-like" action.
U.S. Ambassador to the United Nations John Bolton, meanwhile, told CNN Monday that the U.N. action on North Korea should convince Iran, another country that has attracted global criticism for its secretive nuclear program, to suspend its nuclear activities.
"I hope the lesson they learn is that if they continue to do nuclear weapons they will face the same kind of isolation and friction" that North Korea now faces, he said.
Iran has said its nuclear program is for energy purposes only, not the construction of nuclear bombs.