Pakistan's dependence on China grew as Western export controls and enforcement mechanisms have grown more stringent. China's nuclear assistance predates the 1986 Sino-Pakistani atomic cooperation agreement, with some of the most critical transfers occurring from 1980 through 1985. China is reported to have provided Pakistan with the design of one of its warheads, as well as sufficient HEU for a few weapons. The 25-kiloton design was the one used in China's fourth nuclear test, which was an atmospheric test using a ballistic missile launch. This configuration is said to be a fairly sophisticated design, with each warhead weighing considerably less than the unwieldy, first-generation US and Soviet weapons which weighed several thousand kilograms. Pakistan Foreign Minister Yakub Khan was present at the Chinese Lop Nor test site to witness the test of a small nuclear device in May 1983, giving rise to speculation that a Pakistani-assembled device was detonated in this test.
Evidently, however, the jump-start provided by A.Q. Khan's trove of documents was an insufficient basis for a dependable Uranium program. Chinese assistance in the development of gas centrifuges at Kahuta was indicated by the presence of Chinese technicians at the facility in the early 1980s. The uranium enrichment facility began operating in the early 1980s, but suffered serious start up problems. In early 1996 it was reported that the A.Q. Khan Research Laboratory had received 5,000 ring magnets, which can be used in gas centrifuges, from a subsidiary of the China National Nuclear Corporation.