Police are preparing to destroy are second package linked to chemical explosives found at Australind yesterday.
Police and army divers and other Defence Force personnel have been involved in the operation this morning.
A large amount of sand has been delivered to the area and it appears the chemicals will be buried and blown up in an operation similar to that conducted at Gloucester Park earlier this week.
Police divers appear to have brought the object found yesterday to the surface and are heading back to shore.
Police yesterday said they could not rule out a terrorist plot and are not close to an arrest.
An underwater camera was used to examine the item, believed to be more explosives, that police divers found yesterday near where highly volatile TATP was found wrapped in plastic and tethered underwater to a jetty in Leschenault Estuary on Tuesday afternoon.
The police divers immediately evacuated the area, created a 1km exclusion zone and bomb squad and navy clearance divers were called. They were expected to leave the package submerged last night and blow it up early this morning.
It is believed the preferred method of disposal for TATP is to detonate it where it is found.
The West Australian understands wires were found in the initial packages of TATP, which alarmed detectives as soon as they unwrapped the packages at Curtin House.
It is believed South-West officers believed the powdery substance was a drug and handed it to Perth officers.
WA Police have liaised with Federal agencies, including the Australian Federal Police, since the discovery but refused to say if ASIO was involved.
Acting Cdr Scott Higgins said WA's terror alert level had not changed after the find. But he said police were not close to an arrest and were still looking at all scenarios for why the explosives, which had no legal purpose, were made.
Police are unsure how long the TATP was in the estuary and it is not known if the volatile homemade explosives were being stored in water in an attempt to keep them stable.
Suicide bombers used about 4.5kg of TATP in the 2005 London bombings, which killed 52 people and injured hundreds.
It is understood there was 3kg of it in the packages taken to Curtin House. Murdoch University senior chemistry lecturer David Ralph said TATP, a white crystalline substance, was more stable in water but would explode if subjected to heat, friction or shock.
WA Police Union vice-president Brandon Shortland said he had serious concerns about the procedures, systems and policies surrounding the seizure, transport and storage of chemicals and compounds believed to be drugs.
Premier Colin Barnett said the discovery was serious but he had confidence in police and other agencies to deal with it.
Treasurer Troy Buswell is expected to be near the estuary today for the 50th anniversary of chemical manufacturer Cristal's Australind plant.His visit is expected to go ahead, despite danger nearby.