In recent months, owners Wyldecrest Parks have been creating additional housing spaces on land that was a communal green and by excavating an embankment area.
Concerns the work would weaken the structure of the embankment were first raised by residents in May, and following the discovery of damage at the weekend, worries have been heightened.
>>> Read how residents reacted to the £1.2m redevelopment work here
Melvyn Gardner, who lives on the site with his wife Dorothy, said: "Torrential rain like we've had recently tends to loosen the ground, so we need to know how safe the rest of the posts are.
"We need a Health and Safety assessment. If there had been park homes on the concrete slabs next to the fencing, they would have been damaged, no doubt about it."
But Alfie Best, chief executive of Wyldecrest Parks, which owns the site, said collapse occurred after fencing posts had been deliberately moved by vandals.
He said: " It's not been a landslip, someone has been in the vehicles left on site and has pulled some of the metal posts out of the ground. I'm very upset about it.
"We've had someone down to shore it up, and it will be repaired and put right."
Insisting the fencing in place is fit-for-purpose, he said: "Those metal poles were driven a metre into the ground.
"The amount of earth is not enough to push even a panel fence over. This has been maliciously done."
The work on the park in Stricklands Lane is being carried out under permitted development rules of the council, who in June said any concerns over the retaining fence should be directed towards the Health and Safety Executive.
Now the council's Building Control team has been to visit the banking collapse.
Councillor Bill Evans, Cabinet Member for Planning, Regeneration and City Deal said, “The Council are aware of a collapsed bank at Penwortham Residential site. The Building Control Team have been to the site to assess the situation and to ensure safety cordons are in place.
“The council are now assessing the wider situation and have also alerted HSE.”