Did China know the earthquake was coming?

The quake struck shortly before 2.30pm (1630 AEST), according to the USGS, at a depth of just 10km.

China has denied issuing a warning that a strong earthquake could strike Beijing between 10pm and midnight today (1200-1400 AEST Tuesday).

"We have issued no such warning,'' Li Qianghua, a top official at the China Earthquake Bureau, was quoted as saying by the government's main website.

The People's Daily, the ruling Communist Party's main mouthpiece, had reported earlier on its website that a quake measuring between two and six on the Richter scale could hit Beijing in a few hours.

Link to whole news article about the earthquake which mentions prior warning.

Does anyone else find this strange? Does earthquake detector technology even exist and if so how accurate is it?

Could this be evidence of some sort of secret testing taking place underground which the Chinese Government knew or thought might cause an earthquake of this magnitude?