In a video posted online, the prime minister says the UK can get through the pandemic "together".
Thousands of the devices, which deliver oxygen to the lungs without needing a ventilator, could be made.
The budget airline says it cannot currently give a date for when it will restart commercial flights.
The Duke and Duchess of Sussex reportedly moved from Canada to the US amid the virus outbreak.
Two women and a man are found dead at the property in Hemel Hempstead, Hertfordshire.