The second batch of files, mainly on China's diplomacy between 1949 and 1955, are related to telegraphs between China and Asian countries on recognition of each other, establishment of diplomatic relations and sending ambassadors.
Among other documents, the files included materials about the "Kashmir Princess" event, the official Xinhua news agency reported.
On the night of April 11, 1955, the chartered Air India flight named 'Kashmir Princess' was carrying a small delegation of Chinese and East Europeans, mainly journalists, from Hongkong to Indonesia to attend the Asia-Afro Bandung Conference in Indonesia.
At about 18,000 feet a time bomb detonated in the wheel bay of the plane, blowing a hole in the fuel tank. The flight engineer, navigator and first officer escaped. But the remaining 16 passengers, including seven Chinese cadres and crew members died.
Zhou, who was the main target did not board the plane. His travel plans had been kept secret. In fact, the then Premier did not leave China until April 14, three days after the bombing - when he flew to Rangoon to meet then Prime Minister Jawaharlal Nehru and Burmese leader U Nu before continuing on to Bandung.
The secrecy that surrounded Zhou's travel plans saved his life and doomed the 'Kashmir Princess'. The same plane was scheduled to fly to Rangoon to pick up Zhou for his trip to Indonesia.
Historians have said there is evidence to suggest that Zhou knew of the assassination plot and changed his travel plan though he did not stop a decoy delegation from taking his place.
China declassified for the first time a batch of diplomatic files in January this year.
More declassified files will be opened in batches and by stages, the Foreign Ministry said.
An official with the ministry's archives said that China will open the remaining over 2,000 diplomatic files from between 1949 and 1955 at the proper time, and some of the files from between 1956 and 1960 will be opened in late 2005 or early 2006. According to China's archives law and relevant regulations, historical files should be open to the public 30 years after their creation.
Many in the West saw the Bandung conference as a "gathering of communists and pro-communists.