More than 3,400 people taken to A&E units by ambulance were forced to wait more than an hour to be seen last week.
Figures released by NHS England show the number of ambulance delays of more than 30 minutes went up by a fifth (20%) compared with the previous week, with 14,300 people having to wait more than half an hour compared with 11,900 a week earlier.
Of these, 3,420 were delays of more than 60 minutes, up from 2,340.
The Department of Health says ambulance staff should be able to hand patients over to A&E staff within 15 minutes of arrival at hospital, and not doing so increases the risk to patients due to delays in diagnosis and treatment, as well as the chance a patient will get worse while waiting on a trolley.
There were also 30 cases of ambulances being diverted to other hospitals in the week ending December 17.
An NHS England spokesman said: "The recent cold snap has seen hospitals put under pressure, but they are generally coping.
"Staff are working hard to ensure ambulance handovers are as smooth as possible."