Police said the incident happened just after 11.25am.
A Sussex Police spokesman said: “Police responded to a collision between a vehicle and pedestrian in Chichester Close, Hove.
“The road remains closed while officers, ambulance and fire crews attend the scene.
“It’s not yet clear when the road will re-open. The pedestrian’s injuries are thought to be life-pthreatening.
“Anyone with information which could help officers with their investigation is asked to contact police on [email protected] or call 101 quoting Operation Hourglass.”