Mourners have been warned by the Department for Digital, Culture, Media and Sport (DCMS) not to attempt to join the queue at Southwark Park in south-east London until around 4pm on Friday at the earliest.
The call was made as the official estimate for queuing time reached at least 14 hours.
However, there was some confusion on the ground as hundreds of people continued to file through the gate into the park, with one attendant saying they had yet to receive an order to bar entry.
The DCMS had tweeted: “Southwark Park has reached capacity. Entry will be paused for at least 6 hours. We are sorry for any inconvenience.
“Please do not attempt to join the queue until it re-opens.”
Tens of thousands of people have queued for many hours to see the monarch’s coffin raised on a catafalque in Westminster Hall since it officially opened on Wednesday.
With people waiting through the night to witness the lying in state, the queue had grown to almost five miles long by Friday morning.
But hundreds of mourners were witnessed continuing to enter the park despite the Government’s online warning.
One queue attendant told the PA news agency they had yet to receive any instructions to close the gate and stop any more people joining.
The King and Queen Consort are expected to travel to Wales while the lying in state continues, accessible to the public 24 hours a day.
The couple will attend a service of prayer and reflection at Llandaff Cathedral, before receiving condolences at the Welsh Parliament and meeting members of the Senedd.
They will then travel to Cardiff Castle where Charles will hold a private audience with Welsh First Minister Mark Drakeford and the presiding officer, before attending a reception hosted by the Welsh Government.
The Vigil of the Princes takes place at Westminster Hall, carried out by Queen’s four children (King, Princess Royal, Duke of York and Earl of Wessex).
Eight of the Queen’s grandchildren will stand vigil beside her coffin in Westminster Hall for 15 minutes on Saturday night, royal sources have confirmed.