The Chinese authorities had declared seeking prior permission as a pre-condition for entering the area.
China last week established the East China Sea Air Defence Identification Zone, which includes the disputed Diaoyu islands (known in Japan as Senkaku islands).
It announced that aircraft flying in the zone must abide by these rules or "the armed forces will adopt defensive emergency measures to respond to aircraft that do not cooperate in the identification or refuse to follow the instructions".
On Monday, the US unarmed bombers took off from Guam and the flight was part of a regular exercise in the region, BBC cited US defence officials as saying. Both aircraft later returned to Guam, the officials added.
According to Colonel Steve Warren, Washington had "conducted operations in the area of the Senkakus".
"We have continued to follow our normal procedures, which include not filing flight plans, not radioing ahead and not registering our frequencies," Warren was quoted as saying by BBC.
There had been no response from China, he added.
A Pentagon spokesperson said that the planes had followed "normal procedures".
According to a statement issued by China's defence ministry Nov 23, aircraft flying in the zone "should report the flight plans to the Ministry of Foreign Affairs of the People's Republic of China or the Civil Aviation Administration of China.
Aircraft should "maintain the two-way radio communications, and respond in a timely and accurate manner to the identification inquiries from the administrative organ of the zone or the unit authorised by the organ", the statement said.
The row over the islands, presently being controlled by Japan, has left ties between Tokyo and Beijing highly tense."Setting up such airspace unilaterally escalates the situations surrounding Senkaku islands and has danger of leading to an unexpected situation," Japanese foreign ministry said last week.
Taiwan, which also stake claims over the islands, had expressed regret over China's move.