Shanghai stocks tumbled more than four percent at the open on Wednesday after racking up big gains a day earlier following a week-long break, but Hong Kong clawed back some of the losses of more than nine percent it suffered.

The Shanghai Composite Index shed 4.54 percent, or 158 points, to 3,331, and the Shenzhen Composite Index dropped 4.31 percent, or 90 points, to 2,008.

Both bourses saw big gains the day before but were well off their initial highs.

The Hang Seng Index gained 1.74 percent, or 363 points, to 21,290, having tanked more than nine percent on Tuesday, its biggest loss since the 2008 global financial crisis.

Equities in the mainland and Hong Kong rocketed after China last month began announcing measures aimed at boosting the world's number two economy, piling on more than 20 percent each.

However, a much-anticipated news conference in Beijing on Tuesday – after the Golden Week break – left traders disappointed as officials refused to unveil more stimulus and provided scant detail on the measures already pledged. (AFP)