P&O is the world's fourth largest ports operator

In a statement P&O said the approach valued its shares at 470p, beating the takeover offer of 443p a share it has already agreed with Dubai Ports.

It said it would give PSA until early February to examine its accounts and decide whether to make a formal bid.

Ports are benefiting from expanding Asian exports to the US and Europe.

World trade volumes are expected to grow 7.6% in 2006, according to the International Monetary Fund (IMF).

PSA is wholly owned by Temasek, the Singapore government investment agency, which already owns 4.1% of P&O.

Founded in 1837, P&O has three divisions - ferries, ports and logistics.

In its heyday in the mid-1920s, it owned a fleet of almost 500 ships before transforming itself in the post-war era to concentrate more on cargo shipping and ports.