Hundreds have crowded the Guildhall Square in Southampton to hear Labour leader Jeremy Corbyn say Theresa May is leading a "zombie Government with no ideas, no answers and no leadership".
Southampton Itchen is one of the most marginal seats in the country, with a majority of just 31 votes, which the party held from 1992 to 2015.
Long seen as an impregnable Tory stronghold, the constituency is now 117th on Labour's target list.
Labour leader, Jeremy Corbyn
Mr Corbyn has already visited the Conservative marginal of Hastings & Rye this month, in a bid to take the fight into Tory territory.
It is in preparation for an election which Labour strategists believe could come much earlier than the scheduled date of 2022.
He will also meet supporters in Bournemouth West later, which has been Conservative since 1950 but saw a 6.6% swing to Labour cut the Tory majority almost in half in June.