A yardstick for the US housing market has ticked up by surprise, yet economists aren't ready to call a bottom for the sector.

The National Association of Realtors' index for pending sales of previously owned homes increased 6.3% to 87.7 in December from 82.5 in November, the industry group said.

Pending sales typically close within one or two months of signing. Private analysts projected a 0.5% drop in the December index.

Ian Lyngen, an analyst at RBS Greenwich Capital, said the surprise rise came 'short of signalling a bottom for housing'.

The Australian