Six out of seven hospital trusts in the region with A&E departments have been judged either inadequate or requiring improvement.
Prime Minister David Cameron admitted the record at Kent's Medway Maritime was "not good enough".
Last year, the hospital had some of the worst A&E treatment times in England.
The Gillingham hospital has been in special measures since July 2013.
"That's why we sent in the turn-around team," said Mr Cameron.
"Under this government, we have seen hospitals going into special measures when they have problems but coming out the other end with better management and better results."
The leaders spoke to BBC South East about problems facing the NHS during campaigning visits to the region.
Other hospitals under pressure include Eastbourne District General, which in March was judged inadequate by the Care Quality Commission.
Green leader Natalie Bennett said her party was against concentrating specialist services on one site as had happened in Eastbourne and at the Conquest Hospital in Hastings.
"People want services close to where they live," she said.
"If you have a few big centralised centres you have both economic impacts and real impacts on communities that are losing services they need."
Labour leader Ed Miliband said his party would fund 20,000 more nurses and 8,000 more doctors by raising Â£2.5bn from a mansion tax on properties above Â£2m and raising money from tobacco companies and hedge funds.
"It is a real rescue plan," he said.
"It is big money. The money will flow within months of a Labour government."
Lib Dem leader Nick Clegg said the NHS was under considerable pressure .
"There are lots of complex reasons for that - the main one is we have lots of elderly folk who are spending much longer in hospital because of age-related conditions.
"We need to make sure that when they are ready to be discharged there is a place in the community ready for them to be looked after."
UKIP leader Nigel Farage said he wanted to change the way hospitals were run and managed by having elected boards.
"We are not getting value for money," he said.
"The other problem is that our population has risen massively over the last few years.
"We how have fewer GPs per capita than any other country in Europe."
Leaders of the five main parties in England have set out their plans for the NHS in Kent and East Sussex, where many hospital trusts are struggling.