Two of the victims were "believed to be a mother and her child in a state of embrace buried under the earth", Norazam Khamis, director of the Selangor state fire and rescue department, told reporters on Friday.
The farm did not have a licence to run a campsite and its operators would be punished if they were found to have broken the law, authorities said.
Prime minister Anwar Ibrahim visited the area late Friday and said financial aid would be given to the families of those killed or injured in the disaster.
Selangor state chief minister Amirudin Shari tweeted that all picnic and camping sites in the state would be closed for a week.
Landslides are common in Malaysia after heavy rains, which are regular at the end of the year, and can occur after bouts of bad weather.
However, no heavy rains were recorded in the area on the night of the disaster.
The government has imposed strict rules on hillside development.
In March, four people were killed after a massive landslide triggered by heavy rains buried their homes in a Kuala Lumpur suburb.
In one of the deadliest such incidents, a huge mudslide in 1993 brought on by heavy rain caused a 12-storey residential building outside the capital to collapse, killing 48 people.