One of the bushwalkers managed to get a weak mobile phone signal just after 7am on Monday and sent a text message to say they were safe and sheltering from the cold conditions in a cave south of Katoomba.

Emergency service workers were trying to pinpoint their location in the bush early on Monday morning using GPS co-ordinates, and hoped to rescue them by midday on Monday. Temperatures dropped to seven degrees in the mountains overnight.

The hikers, aged between 27 and 69, had set off at 8.30am on Sunday and were last seen about 1pm on Narrow Neck Plateau, police said.

They were due to return at 5pm on Sunday but, when they still had not returned by 7pm, concerned relatives raised the alarm.

Police and emergency service workers launched a search on Sunday night from the Golden Stairs and scoured the area until 1.30am on Monday, but found no trace of the group.

The NSW Ambulance helicopter was also involved in the search until 1am.

Inspector Ken Shack-Evans, from the Blue Mountains local area command, told ABC radio on Monday that none of the group was injured but their exact location had not been confirmed.

"We have now been in touch with that group of walkers. They are all safe and well, there's no injuries reported to us and they have spent the night huddled together in a cave down there in the bush," he said.

"The bushwalkers have been told to stay put and not to attempt to try and walk to another location."

He said the seven bushwalkers had some experience, but were not prepared to spend a night in the bush and were not carrying an emergency beacon.

"They certainly weren't dressed for overnight activities. Between the seven of them they only had two torches," he said.

Once the group's location is confirmed, police and paramedics will attempt to reach the group and walk out with them.