A person claiming to be in a vehicle on the A414 at North Weald, Essex, called police at 08:30 BST on Wednesday to say it had earlier been in Ashford in Kent.
The lorry was found by Bedfordshire Police at Toddington Services, on the M1, in the afternoon.
Six people are being held in custody.
Supt Trevor Roe, from Essex Police, said it was a "positive outcome".
"We've seen with human trafficking....the events could turn out to be very tragic so I think it was important we reacted fairly quickly across our neighbouring forces to try to locate the vehicle," he said.

The aircraft, nicknamed "Bette" after one of its pilot's girlfriends, was built in 1941 from donations from the Borough of Lambeth Spitfire Fund.
It was stationed in Cornwall, Hampshire, Norfolk and Shropshire during the war but crashed in 1944.
Bidding stalled below its Â£120,000 to Â£150,000 valuation.
The aircraft saw service with four RAF squadrons between 1941 and 1944 and was flown by author Alec Lumsden, who gave it the name Bette and added a character from the Daily Mirror cartoon strip 'Just Jake' to the paint work.
After it crashed in Shropshire in September 1944, killing its Australian pilot, its wreckage was taken to Ibsley museum, Ringwood, Hampshire and displayed.
The aircraft was later passed to a collector who showed it at events. It has also been immortalised by modelmakers Airfix and Revell.
John Tomlin, from Historics at Brooklands, said: "The historical side of war birds is an up-and-coming market. There are now about 42 flying Spitfires and this seems to be increasing ever year.
"The rarity, the history and the provenance of all these aircraft make them very investable items and they're investments that can be used and enjoyed by a lot of people."
Experts believe it would cost about Â£1.8m to fully restore the plane.

He told MPs the UK would never be a world-beating economy unless young people were better educated.
And he called for "much bigger devolution to the people who know where the [failing] schools are".
On improving literacy and numeracy, he added: "We need it across the country and we need it yesterday."
The Conservative grandee, who was deputy prime minister in the 1990s and subsequently advised David Cameron on regional strategy, made the comments as he gave evidence to the Commons Business Innovation and Skills Committee alongside former chancellor George Osborne.
Claiming that the UK is "29th as a country in the world league of education" - it was 23rd in reading in 2015, according to the OECD's Pisa rankings and 26th in maths - he stressed: "If we accept that - we'll never be a world beating economy in the future because it's all about people - it's about education and then about skills.
"And if you want to have skilled people, you'd better educate them properly before you start making them skilled."
Lord Heseltine, whose leadership challenge helped trigger Margaret Thatcher's departure from Downing Street in 1990, said standards need to be set by a strategic commission, chaired by the prime minister "that are relevant to the best in the world and not the 29th".
"If I could design an industrial strategy it would start in the primary schools," he said, adding that about a quarter of children leaving primary schools are "illiterate and innumerate" by modern employment standards.
"My own view is clear - there needs to be a much bigger devolution to the people who know where those schools are and they know the people that run them and they know where the inadequate results are coming from - in my personal experience of life: show me the problem, show me the person in charge."
Lord Heseltine cited one success story - Northamptonshire's "Race to the top" initiative - which aims to make Northamptonshire one of the highest performing counties for education by 2020.
"We spend a lot of time discussing the theories of education and the structures of education, but what we want is good head teachers," he said.
"Wherever you go in this country there is a skills shortage - that is a serious problem facing the expansion of the economy and it's a highly centralised process - not devolved on the scale that it would seem to me reflect the market opportunities."
Four suspected illegal immigrants are on the run after a lorry containing ten people was discovered by police following a "distress" call from one of the people inside.
[NEXT_CONCEPT]
The fuselage of a World War II Spitfire that has spent the last few years in a garden in Oxford has failed to reach its asking price at auction in Surrey.
[NEXT_CONCEPT]
Lord Heseltine says the UK's skills shortage is a serious problem - and if it was up to him he would start industrial strategy in primary schools.