The Kibarani dumpsite was grabbed in 1994, subdivided into four parcels and allocated to three companies, the National Lands Commission has said.
Chairman Muhammad Swazuri said the plots were illegally and irregularly allocated to Ancient Inland Seas Ltd (0.4ha and 1.3ha), Halid Ahmed (0.5ha) and
Mtech Ltd (2.6ha).
Swazuri said seven parcels stretching into the Indian Ocean have also been allocated.
"Ocean water cannot be allocated and this is straight illegalities," Swazuri said during a fact-finding mission at the area on Friday.
The tree owners, Swazuri said, will be given seven-day notice from August 6, to produce documentation to showing how the land was acquired.
Inquiries will be held from August 15 in Mombasa amid revelations by Swazuri that four Green Cards for the Kibarani parcels have disappeared.
The card is one of the documents used to prove land ownership and is in the custody of the Lands ministry.
"People normally do such 'ukarabati' (funny schemes) when there is a dispute," Swazuri said.
During the tour, it emerged that the land in question is part of the 32 acres parcel which was formerly a holding ground for ministry of Livestock and Veterinary Services.
This land has now been subdivided into 55 parcels, including the ones at Kibarani. The holding ground was government's alienated land demarcated from 1920-1954.
"There is no record that the government de-gazetted the land as the holding ground," Swazuri said.
The sub-division for the larger parcels begun in 1987 and by Thursday, only eight acres had remained.
"The 55 parcels will be scrutinised and a verdict will be issued," the NLC boss said.
President Uhuru Kenyatta recently asked the Lands boss to revoke the Kibarani titles and reserve the land for the Mombasa regeneration project.
He said that the dumpsite be transformed into a recreational site in line with the Mombasa regeneration project.
This followed after his meeting with Mombasa Governor Ali Hassan Joho, Cabinet Secretaries Najib Balala (Tourism) and Keriako Tobiko (Environment).