A second location is being searched by gardaí investigating the disappearance and murder of Fiona Pender.
The operation, in the Slieve Bloom Mountains in Co Laois, will continue overnight.
Excavation work is being carried out in a forested area, close to the village of Clonaslee.
Portable floodlights have been brought on site.
In December 2014, a search took place in the Slieve Bloom Mountains after credible information was given to gardaí.
However, a two-week operation found no trace of Ms Pender, a hairdresser and former part-time model.
Gardaí completed a search of bogland near the village of Killeigh in Co Offaly yesterday as part of the investigation.
They said they were not releasing the results for operational reasons.
It is understood that gardaí are acting on information they received as part of their inquiries.
Ms Pender, who was 25, went missing from her flat on Church Street in Tullamore, Co Offaly on 23 August 1996.
She was seven months pregnant at the time.
Earlier this week, gardaí confirmed the case had been reclassified from a missing persons investigation to a murder inquiry.
However, sources close to the investigation said the case was always treated as murder.
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Five people were arrested in 1997 as part of the inquiry, but no one has been charged.
The Irish Aviation Authority has restricted the use of drones over the search area in Co Laois and the Ross Road at Clonaslee will remain closed from the R422 to the R440 junctions.
Gardaí said that no through traffic will be allowed onto the road until further notice, with local access available to residents via the R422 entrance.
They renewed their appeal to people who previously came forward, but felt they could not provide all of their information, to contact the investigation team again.
