Asian stock market, after the Japanese government said the damage from the deadly tsunami and earthquake could amount up to $308 billion.

Markets were kept edgy by news that the crippled Fukushima nuclear plant was emitting black smoke and by reports of rising levels of radiation in Tokyo's water system, even as Japan made progress in tackling the nuclear crisis.

"It's a great unfathomable about when one can feel reassured that the situation at Fukushima has been brought fully under control, and secondly what is the cost, and how is it going to be financed, and what are the supply chain effects going to be," said Marc Ostwald, strategist at Monument Securities.

Investors were also kept on the defensive by uncertainty over the ongoing conflict in Libya and concerns that unrest in Yemen may spread to neighbouring countries in the oil-rich.