A tale of two Asian share buy-backs: one economically rational, the other less so. Monday's announcement from Li Ka-shing's Hutchison Whampoa that it might make an offer to buy out minorities in a phone unit came as little surprise. Hong Kong-listed Hutchison Telecommunications International, spun off six years ago and then hollowed out by disposals of its best assets, is trading more than three times cheaper than peers on a price/book basis. This is how tycoons operate: buy low, sell high.

The justification for the other is less obvious. Yesterday's disclosure from PetroChina that its unlisted parent CNPC had bought back just under half a billion shares was mysterious, first, for its timing – months after the purchases were made, between September 2008 and September last year. Buying back 6 per cent of the Shanghai A-shares and 1 per cent of the Hong Kong H-shares lifts CNPC's ownership of PetroChina to 86.54 per cent from 86.29 per cent – an infinitesimal difference. Average prices over that period suggest state-owned CNPC spent about $600m at a time when neither share needed much support.

The best explanation is a creeping renationalisation of the state's most prized strategic assets. China has used the crisis, and the stimulus it prompted, to re-assert state control, often through forced mergers in bloated industries. Any diminution in the free float of the world's biggest company by market capitalisation should be seen in the context of the doctrine of guojin mintui – “the state advances as the private sector retreats.”