A Bloomberg report Tuesday put some numbers on the plan, citing people close to the matter.

It said policymakers want to mobilize about $279 billion as part of a stabilization fund to buy shares onshore.

The money will reportedly come mainly from offshore accounts of state-owned enterprises.

Chinese stocks were up and down on Tuesday following the report.

Shares rose immediately after the news, then slipped lower, only to later turn up again.

Hong Kong's Hang Seng index closed 2.6% higher in the end - its biggest one-day gain in two months.

The Shanghai Composite index rose a more modest 0.5%.

China's markets have had a bad start to the year.

Foreign investors have stayed away due to patchy economic growth and data pointing to more property market turmoil, including a new slump in home sales.

On Monday, the government said it would step up mid- and long-term fund injections in the capital market.

It said it wanted to strengthen stability and promote healthy development.

But one leading investor said that while the move was welcome, they feared it was still inadequate due to being under 2% of GDP.

Overseas funds have sold roughly $1.6 billion in Chinese equities so far this year, according to Morgan Stanley.

Chinese investors have also largely avoided stocks.

The country's Securities Regulatory Commission did not respond to a Reuters request for a comment on the latest reports.