A man has been critically injured after being hit outside his car on the motorway.

Emergency services were called to the Logan Motorway about 11.55am in Forest Lake, Brisbane, after reports a blue Kia Cerato, stopped in the emergency bay, had been struck by a white Kia Cerato.

Initial inquiries indicate the male driver and sole occupant of the blue Kia was outside his vehicle at the time of the crash, Queensland Police Service said.

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He sustained life-threatening injuries.

The driver of the white Kia, a woman in her 30s, is assisting police with their investigation.

Authorities are urging anyone with dashcam footage of the incident, or of either vehicle in the moments leading up to the crash, to come forward.

Investigations are ongoing.