An Iraqi family was detained while running across the A12 motorway on Wednesday night (16 August).
A man, a woman and four children were arrested by Essex police after they were spotted jumping down from a lorry at around 8pm on the A12, near the Hatfield Peverel turnoff.
Police closed the dual carriageway for around 20 minutes as officers searched for the immigrants.
The National Police Air Service in Boreham said it was assisting police in the search.
A driver who was travelling to Colchester told The Daily Gazette: "We just ground to a halt a little before Hatfield Peverel. I saw a helicopter circling for ages. At first I thought there had been a crash and it was the air ambulance. It kept hovering over the fields either side of the A12."
"We were stopped for about twenty minutes and a few police cars went past," he added.
The family was handed over to immigration enforcement. The Home Office said it will review the six Iraqis' cases in line with immigration rules.
"Where someone has no right to remain in the UK, we will take action to remove them," a spokesperson for the Home Office said.