In what appears to be the first time a Boston ICU has reached capacity in the coronavirus pandemic, Boston Medical Center was treating so many patients who needed intensive care on Sunday that it had to stop accepting new patients into the ICU during the overnight hours, the hospital says.

The worrisome milestone comes at a time when state, federal and local officials are warning that the viral outbreak may be entering a surge period in Massachusetts and other states.

BMC says that overnight Sunday, ambulances brought patients to other hospitals instead. By Monday, the hospital says, it was able to begin accepting ICU patients again.

Boston health officials say this is the first known case of a Boston hospital reaching ICU capacity during the current COVID-19 crisis.

According to numbers reported Monday by the Massachusetts Health and Hospital Association, Boston Medical Center has 140 COVID-19 patients with 39 in the ICU. On Sunday, the group says the hospital had 147 COVID-19 patients with 42 in the ICU.