The charitable foundation established by Nina Wang, the Hong Kong tycoon, fired its first shot in the battle for her $3.9bn (€2.6bn, £2bn) estate on Friday, taking aim at a reclusive businessman who also claims to be her heir.

The Chinachem Charitable Foundation filed court papers in Hong Kong arguing that Ms Wang, who died last April, might have been too ill in late 2006 to approve a will that bequeathed her estate to Tony Chan. Ms Wang was diagnosed with cancer in 2004.