"We will soon seek permission from the government for a survey. As per the current plan, surface exploration is scheduled in a four sq kilometre radius around the shrine," Director of state Archaeology Department G Premkumar told PTI.
A detailed excavation would be carried out in the explored sites later if necessary.
"On getting approval, we will identify locations for the surface exploration. Except for hearsay and local lore, no authentic studies have been conducted to ascertain the antiquity of the temple. We hope the initiative will give us a scientific lead in that direction," Premkumar said.
Lord Vishnu is seen in a reclining posture in Sree Padmanabhaswamy Temple.
Experts of the department carried out a mini excavation at the north entrance of the historic temple last week, after the sighting of remnants of centuries-old stone pavement and steps.
A top official said the current round of excavations have been concluded and a detailed report on that would be submitted to the state government tomorrow.
"It was a mini excavation. Now we are planning to conduct a detailed surface exploration of heritage sites in places around the shrine," Premkumar said.
The magnificent temple, renowned for the priceless treasures stashed in its underground vaults, was renovated by 18th century Travancore king Anizham Thirunal Marthanda Varma.
It was built on marshy land after elevating the surface, he said.
An architectural splendour in granite, the grand temple is a fusion of different styles.
It is one of the few Hindu temples where Lord Vishnu is seen in a reclining posture.