Disabled People Against Cuts (DPAC) said about 150 people, many in wheelchairs, had supported the protest to call for better financial support.
It also wants the immediate publication of a UN report into the government's handling of disabled people's rights, which is not due until 2017.
The government said it spent Â£50bn supporting disabled people annually.
The Department for Work and Pensions said it knew more needed to be done to support people with disabilities or health conditions.
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Ellen Clifford, from DPAC, said the protest had formed part of a week of action to highlight changes to Personal Independence Payments (PIP) to help people aged 16 to 64 cope with extra costs, as well as cuts of up to Â£30 per week for some people who claim Employment Support Allowance (ESA).
"It's the opening of the Paralympics tonight and we're celebrating all the athletes, but the cuts that they're [the government] bringing through are meaning other peoples' lives are going dramatically backwards," she said.
"Some are facing cuts to PIP, ESA, as well as their social care and their dignity too."
She said the protest had been well-supported but "there's a disproportionate amount of policing here, we're surrounded by police".
"We've got wheelchairs, the police have got bolt cutters. They've arrested someone's personal assistant and threatening to arrest everybody," she said.
Scotland Yard said it had arrested two people for obstructing a public highway.
A protest over disability benefit cuts has closed London's Westminster Bridge and two people have been arrested.