It was feared more than 30,000 litres (7,925 gallons) of sulphuric acid had spilled after all 26 carriages of a freight train carrying the chemical derailed in remote northern Australia, authorities said on Tuesday.
The train, belonging to locally listed freight firm Aurizon Ltd, was carrying about 819,000 litres (216,360 gallons) of sulphuric acid, four times the amount first estimated, when it derailed in Queensland state on Sunday.
"One of the carriages has likely ruptured and it is possible that up to 31,500 litres of acid has leaked out," Queensland Police said in a statement.
Testing by the Department of Environment and Heritage Protection suggested that a nearby waterway had not been adversely affected by any leak, the statement said.
Aurizon said in an email to Reuters the cause of the incident was not yet known. Three train drivers had received minor injuries but had been released from hospital, it said.
A derailment and chemical spill adds to pressure on the haulage company after a downturn in coal shipping volumes forced it to issue a profit warning last week, sending its shares sharply lower.
It would also disrupt mining companies already slashing production volumes to cope with weak commodity prices. Miners use sulphuric acid to separate and clean some minerals.
The train was traveling from the east coast port city of Townsville to Phosphate Hill, 1,000 km (620 miles) inland, Aurizon said.
The police statement did not give a cause for the derailment but said the area had experienced flooding, causing a nearby highway to be cut off.
Police said they had formed a 2-km (1.2-mile) exclusion zone around the crash site to help salvage crews gain access.