Southampton's proposed Titanic museum could result in the closure of the city's maritime museum.

The opening of the attraction, provisionally called the Sea City Museum, is planned for April 2012. This is the 100th anniversary of the sinking of the Titanic, which sailed from Southampton. Southampton Maritime Museum, which is housed in the medieval Wool House, has a Titanic exhibition, but the new museum would display 4,000 stored artefacts.

The city's major projects manager, Tina Dyer-Slade, said: "The other museums' fate has yet to be determined."

The Heritage Lottery Fund (HLF) has awarded £500,000 towards the estimated £28m cost of converting former magistrates' court and police headquarters at the city's Civic Centre into the museum. Southampton City Council will now apply for another £4.5m from the HLF.

Meanwhile, a dispute over hours has led to the closure of Southampton Maritime Museum, Southampton City Art Gallery and the Museum of Archaeology on Sundays and bank holidays. Staff are refusing to accept seven-day working as contracted hours, rather than overtime. The council said it hoped for a resolution by "early June".