A group was seen jumping from the back of a lorry and into cars days before 39 people were found dead in a lorry container nearby, a jury heard.
Stewart Cox said he was on his way to work when he saw 10 to 20 people "with rucksacks" run from the lorry towards the four cars on 11 October 2019.
The bodies of 39 Vietnamese people were found in a container on a nearby Essex industrial estate 12 days later.
Four men are on trial at the Old Bailey in connection with the deaths.
Prosecutors have said the bodies of men, women and children, aged between 15 and 44, were found when the container was opened in Purfleet, Essex.
Temperatures in the unit reached an "unbearable" 38.5C as the Vietnamese nationals were sealed inside for at least 12 hours, jurors were told.
Giving evidence, Mr Cox said he was trying to go to work at about 08:00 on Friday, 11 October 2019, but in the narrow lane in front of him was a lorry with a red-and-white cab, and four Mercedes cars which had just pulled up.
"I just see people getting out of the back of the lorry… with rucksacks… and just running towards the cars to get in the cars," he told the jury.
"After they disappeared the lorry, he was in a real hurry to get out.
"He pulled into the lorry park and then reversed. I tried to get a picture, but I just panicked. There was no number plate on it. It was covered over."
The jury has seen CCTV from the nearby Orsett Golf Course that morning showing a red-and-white lorry, two Mercedes cars, an Audi and another car driving down the lane "in convoy," according to the prosecution.
The prosecution has said a picture from nearby Purfleet Port that morning shows Christopher Kennedy collecting a lorry trailer that had crossed the channel unaccompanied from Zeebrugge in Belgium.
Prosecutors allege the trailer had been dropped off in Zeebrugge by Eamonn Harrison.
The prosecution say that 12 days later he also dropped off the trailer in which the 39 people died.
Mr Harrison, 23, of Mayobridge, Co Down, Northern Ireland, and Gheorghe Nica, 43, of Basildon, Essex, are on trial accused of manslaughter.
The pair are also accused of being part of a people-smuggling conspiracy with Mr Kennedy, 24, of Co Armagh, Northern Ireland, and Valentin Calota, 37, of Birmingham.
The trial continues.