The overall proportion of hospitals declaring alerts under the NHS operational procedures escalation framework rose only slightly in the five days to 13 January compared with the previous week, according to data published on 20 January.
But the proportion of trusts that declared a level four alert - the highest possible warning - rose from six in the first week of 2017 to 27 in the second week, analysis by GPonline shows.
Declaring a level four alert indicates that a hospital is facing severe, rising pressure and that it is 'unable to deliver comprehensive care'. NHS England guidance warns of 'increased potential for patient care and safety to be compromised' where hospitals are at this level.
GP leaders warned that the NHS crisis reflected a system with no spare capacity being stretched beyond its limits by winter pressure. Practices are facing extra workload from patients re-attending because of delayed hospital appointments, the BMA said.
GPC deputy chair Dr Richard Vautrey told GPonline: 'The declared pressure on hospitals is a sign of the workload pressure being experienced right across the NHS, not least in general practice.
'It's the inevitable consequence of running at full capacity for the whole of the year and having little or no spare capacity to respond to the predictable increased pressures of winter. In addition delays in hospital routine activity leads to additional pressure on practices as patients asttend worried about the consequences of cancelled or delayed appointments.'
A total of 12 of the hospitals that declared a level four alert were in the Midlands and East NHS region, and the remaining 15 in the South of England region - the worst affected area overall.
Just one trust in the London region declared an alert - at level three, while 16 trusts in the North of England region reported level three alerts. Level three alerts indicate major, increasing pressure that is 'compromising patient flow'.