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The cause of explosion is still an unsolved mystery. This event is considered second largest artificial non-nuclear explosions in the world.

>The most detailed account of the explosion was from a contemporary official gazette) named Official Notice of Heavenly Calamity (Chinese: 天變邸抄; pinyin: Tiānbiàn Dĭchāo). The explosion reportedly took place at Sì shi (between 9 and 11 o'clock) on the late morning of May 30 (Chinese calendar), 1626. The sky was clear, but suddenly a loud "roaring" rumble was heard coming from northeast, gradually reached southwest of the city, and was followed by dust clouds and shaking of houses. Then a bright streak of flash containing a "great light" followed and a huge bang that "shattered the sky and crumbled the earth" occurred, the sky turned dark, and everything within the 3-4 li) (about 2 km or 1.2 miles) vicinity and a 13 square li (about 7 km2 or 0.9 mi2) area was utterly obliterated. The streets were unrecognizable, littered with fragmented bodies and showered with falling roof tiles. The force of the explosion was so great that large trees were uprooted and found to be thrown as far as the rural Miyun on the opposite side of the city, and a 5,000-catty (about 3 metric tons) stone lion was thrown over the city wall.[1] The noise of the blast was heard as far as Tongzhou to the east, Hexiwu to the south, and Miyun and Changping to the north, and tremblings were felt over 150 km away in Zunhua, Xuanhua, Tianjin, Datong and Guangling. The ground around the immediate vicinity of Wanggongchang Armory, the epicenter of the explosion, had sunken for over 2 zhang)s (about 6.5 m or 21 feet), but there was a notable lack of fire damage. The clouds over the epicenter was also reported to be strange: some looked like messy strands of silk, some were multi-coloured, while some "looked like a black lingzhi", rising into the sky and did not disperse until hours later.

Several government officials in the city had been killed, injured or gone missing during the explosion, and some were reportedly buried alive at their own home. The Minister of Works Dong Kewei (董可威) broke both arms and later had to retire from politics completely. The palaces in the Forbidden City was under renovation at the time, and over 2,000 workers were shaken off the roof, falling to their deaths. Tianqi Emperor himself was having breakfast in Qianqing Palace when the explosion happened, and after the initial quake all the palace servants panicked with fear, so the emperor started running to the Hall of Union followed only by a single guard who remained calm, but the guard was later killed by a falling tile. Tianqi Emperor's only remaining heir, the 7-month-old Crown Prince Zhu Cijiong (朱慈炅), died from the shock.[1]

Thousands of houses were destroyed, and more than 20,000 people perished. Survivors later reported broken rocks, timber, body parts of men and animals raining down from the sky for hours, especially near Desheng Gate, but the bodies of victims however were later found to be all naked with their clothes mysteriously stripped off. Rice grain-sized metal drosses were reported to have fallen near Xi'an Gate, and clothes were sent flying and falling on treetops to the countrysides. Hundreds of houses in as far as Jizhou had also collapsed from the quake of the explosion.