The character of Balluta Square would be spoiled if a proposal by the St Julians council for an underground car park went ahead, according to Din l-Art Ħelwa, the heritage trust.
"The square should remain intact... none of its charming features should be removed nor any trees cut down to make way for the construction of an underground parking lot," the NGO stressed.
It insisted that a shelter and a row of buses parked on this stretch of the road would create an unacceptable eyesore for residents and other pedestrians enjoying the charming ambience of the square.
The proposed bus parking sites should be located away from the historic site.
DLĦ was reacting to the proposal for an electric bus terminus and underground car park submitted by the St Julians council, which has provoked heated opposition from concerned residents.
The Labour Party has also warned the square would be under threat if the planning authority approved the application to develop a "green urban transport terminal".
Council mayor Peter Bonello has tried to allay fears by saying the official public consultation had not started and he guaranteed this would happen at the "appropriate time".
Under the proposal, the electric bus terminus would partly replace the existing public toilets. A covered shelter would stretch up the road that divides the square from the valley. It is proposed that this long shelter would have rows of solar panels installed on the roof and buses parked underneath.
Balluta Square and several nearby buildings, including the historic Balluta Buildings and Villa Casa Torregiani on either side, have been scheduled by the Malta Environment and Planning Authority. This protection extended to the square itself, with its old kiosk, monument and fountain, DLĦ said.
Meanwhile, 13 residents and shop owners yesterday sent a letter to Prime Minister Lawrence Gonzi expressing concern about the "persistent rumours" that the old oak trees in Balluta Square had been "declared sick and condemned to be uprooted".
They claimed the real reason for the trees' removal was to make way for the underground car park, which would destabilise the square and risk harming the Balluta Buildings.
"We would appreciate if you can put our minds at rest that the people of St Julians will be allowed to retain such an important open space with its mature local trees. We remind you of the importance of not destroying existing shade trees in the area, which is frequented by all, including the elderly, and families with small children."
The letter was coped to Rural Affairs Minister George Pullicino and to the Parliamentary Secretary for Local Government, Chris Said.