The accident and emergency department in Northwick Park Hospital, in Watford Road, remains closed to ambulances following a fire yesterday.
Walk-in patients are being treated at A&E, however operations and some outpatients appointments have also been cancelled at St Mark's Hospital.
Chief executive of the North West London Hospitals NHS Trust which manages the hospitals, Fiona Wise, said: "Our staff, the fire brigade and other emergency services acted very quickly and have been tremendous. All our patients are safe and there have been no injuries as a result of the fire.
"Patients and their relatives have also been very understanding and my thanks goes out to them."
The 250 patients who were evacuated from the building were moved to other wards and Central Middlesex Hospital, in Park Royal. While 90 other patients who were well enough to go home were discharged.
The maternity department has now reopened after being closed following the blaze, which affected the main ward block and water supplies.
The areas which are currently closed are Dray, Haldane, Frederick Salmon and Jenner wards, as well as the theatre admissions unit, regional renal unit and the endoscopy and catheter lab.
Anyone worried about relatives can call 020 8869 2444 for more information or visit http://www.nwlh.nhs.uk