Officers and “territorial support” police vans were seen outside the building in Southwark on Friday.
Protest group Southwark & Lambeth Anti-Raids said it believed the people placed at the hotel in New Kent Road were set to be relocated to the barge moored in Portland, Dorset.
It put out a call for more protesters to join the action.
A Metropolitan Police spokesman said: “Officers are remaining at a protest in New Kent Road, SE1. No arrests have been made.”
A Home Office spokesperson said no people would be removed from the hostel on Friday.
They added: “Housing migrants in hotels costs £8 million a day. We have returned 150 hotels to local communities and the public would expect us to make use of alternative accommodation sites which reduce costs for the taxpayer.
“The police have extensive public order powers to tackle any potential disorder at protests and have our full support in doing so.” Southwark & Lambeth Anti-Raids helped rally protesters to the large demonstration in Peckham last week, in which 45 people were arrested.
Police clashed with crowds attempting to stop a coach leaving for the Bibby Stockholm.
Activists surrounded the bus at a hotel at about 8:40am on Thursday and its tires were let down.
At about the 3pm it was forced to leave without any asylum seekers on board.
The Bibby Stockholm has been as accommodation since last August as ministers sought to find alternatives to costly hotels while migrants await decisions on their asylum applications.
But the vessel has been plagued with issues, including an outbreak of Legionella bacteria on board.
In December it was confirmed that one of the people on board had died, with reports suggesting he had taken his own life.
In February, MPs warned "claustrophobic" conditions on board could amount to a breach of asylum seekers' human rights.
