A developer is looking to build a new 40-story mixed-use building that would bring hundreds of hotel rooms and residences, along with retail and restaurants, to Boston’s West End. 

The RMR Group LLC submitted a letter of intent with the city of Boston Planning Department on Aug. 28 for construction of the project at 251 Causeway St. 

The hotel and residential project is located in Boston’s Bulfinch Triangle neighborhood and will encompass three adjacent parcels: 251 Causeway St., 100 North Washington St. and 126 North Washington St. 

The 30,000-square-foot project site currently houses a 143,000-square-foot office building, a 56,000-square-foot office building and a six-unit residential apartment building. According to the filing, the office buildings are nearly empty and attempts to find new tenants have been unsuccessful.

If approved, the 600,000-square-foot, 40-story mixed-use building would include 300 hotel rooms, 420 residential units and 30,000 square feet of retail, restaurant and amenity space. There would also be a three-level, below-grade parking garage. 

The Newton-based developer said the project “will deliver much-needed housing, as well as hotel and retail uses and public realm improvements that will activate Causeway, North Washington and Medford Streets,” as well as “revitalize this critical edge of the Bulfinch Triangle and optimize its potential given its proximity to transit infrastructure, cultural and entertainment uses, and open space.”

The project will also reflect the city’s objectives for climate sensitivity and readiness in its design and operation, according to the filing.

The developer anticipates submitting a project notification form later this month.