The beach between Lowestoft South Pier and Parade Road South has been eroded, and now part of the ramp at Children's Corner is crumbling.
Waveney District Council said it believed the ramp could collapse.
A barrier has been put across the prom at the ramp's entry, and another at a groyne to the south of the ramp.
A spokesman for the council said it would probably be closed for several months.
The council said there were also concerns about part of the shoreline over the Royal Green frontage as far as Parade Road South.
Old sea defence debris, including pieces of steel and timber, littered the beach, the spokesman said.
The risks were being looked at, and it it was possible restrictions over public access could be put in place.
Part of a Suffolk beach has been closed to the public amid safety fears after damage caused by unusually rough seas and high tides earlier this month.