Police investigate spilt package

Police are investigating the origin and intended destination of a package of corrosive solvent that caused the evacuation of a western Sydney mail distribution centre when it was spilt.

A woman was taken to hospital and about 150 workers were forced to leave the Australia Post international mail centre at Granville when a package containing about a litre of liquid was spilt in a Customs sorting area on Wednesday afternoon.

"We've identified it as being a corrosive solvent," Fire and Rescue NSW Superintendent Ian Krimmer told AAP.

"It needs to have some more testing before we can finally determine what it is."

Nine workers were assessed by paramedics.

Fifteen firefighters are at the scene using sand to soak up the spilt chemical.

Supt Krimmer said they expected to finish by about 8.30pm (AEDT) and workers would be able to return to the mail centre shortly after.