The Prime Minister has called for those involved in the death of 39 people whose bodies were found in a lorry container to be "hunted down and brought to justice".
Police were called to the Waterglade Industrial Park in Grays at 1.40am today by paramedics.
The victims, found in the container believed to be from Bulgaria, are thought to be 38 adults and one teenager.
Essex Police said the lorry driver, a 25-year-old man from Northern Ireland, has been arrested on suspicion of murder.
During PMQs, Thurrock MP Jackie Doyle-Price said: "To put 39 people into a locked metal container shows a contempt for human life that is evil. The best thing we can do in memory of those victims is to find the perpetrators and bring them to justice."
Responding, Mr Johnson said: "It is hard to put ourselves in the shoes of those emergency services, as the right gentleman opposite (Jeremy Corbyn) said, as they were asked to open that container and to expose the appalling crime that had taken place.
"I must say I do share her strong desire now for the perpetrators of that crime, and indeed all those who engage in similar activity - because we know that this trade is going on - all such traders in human beings should be hunted down and brought to justice."
Home secretary Priti Patel described the discovery in Essex as "truly shocking".
"From what police have been able to ascertain so far is that the vehicle is believed to be from Bulgaria and entered the country at Holyhead, North Wales, one of the main port or ferries from Ireland [sic] on the 19th of October," she told the Commons.
"Essex police have now launched a murder investigation.
"A 25-year-old man from Northern Ireland has been arrested on suspicion of murder. He remains in police custody as enquires continue.
"I think the whole house will agree that this is a truly shocking incident.
"My thoughts are with the victims and their loved ones at this utterly terrible time.
"While the nationalities of the victims are not yet known, I have asked my officials to work closely with the investigation, providing all assistance we can in these horrific circumstances."
Essex Police has set up a casualty bureau for anyone to call if they have concerns about relatives who may be involved.
Aerial footage from the scene shows forensic officers walking in and out of the lorry and two tents have been erected - one in front of the lorry and one behind it with police vehicles on either side.
Police have taped off the area as they investigate.
Reporting by PA.