The first happened at about 3.30pm at Km 78 of the Lahad Datu-Felda road where a 44-year-old man died while his wife and a friend suffered head injuries.
District Police Chief ACP Shamsudin Mat said the deceased, identified as Abdul Wahab Ali, succumbed to serious injuries at the scene.
It was learnt that they were travelling in a Proton Saga heading to Kampung Embara Budi from here when they collided with a tanker lorry.
"Preliminary police investigation showed the tanker lorry that was heading towards Lahad Datu from Felda Sahabat went out of control and crossed into the opposite lane before colliding with the Proton Saga.
"The impact of the crash caused the driver of the Proton Saga to be trapped inside his car," he said, adding the two other victims travelling with Abdul Wahab were taken to the Lahad Datu hospital for further treatment.
The case would be investigated under Section 41(1) of the Road Transport Act 1987.
In KUNAK, two men died while two others injured, one of them seriously, when their Kancil collided with a 4WD Nissan Navara at Km 5, Kunak-Tawau road, near the Simpang Empat stalls, about 11pm on Monday.
The deceased was identified as Sgt. Pangkuma ak Bedie, 42, from Kunak Police Station and a senior citizen Wong Hong Hang, 71.
The driver of the Kancil, identified as Richard, 51, a fireman, sustained serious injuries and was warded in the Intensive Care Unit (ICU) at the district hospital.
It was learnt that the Kancil was making a turn at the junction while the Nissan Navara was coming from the Tawau direction.
Kunak Police Chief Supt. M Radzali Mahmud confirmed the incident and that it was being investigated under Section 41(1) of the Road Transport Act 1987.