Seven suspects, aged from 48 to 76, were detained on suspicion of conspiracy to burgle on Tuesday morning, a police statement said.
Two more suspects, aged 43 and 58, were detained later Tuesday in north London on the same grounds.
More than 200 officers who raided a dozen properties in north London and in Kent, south of London, on Tuesday morning recovered "a number of large bags containing significant amounts of high value property," the police said.
The men have been taken to a London police station for questioning, police said. Searches of the properties are continuing.
The seven suspects arrested in the morning were described as all being British.
Police: Officers worked 'relentlessly'
Thieves broke into the vault of Hatton Garden Safe Deposit Ltd. over the Easter holiday and may have been able to take as long as four days to rifle through the boxes.
They used a drill to bore through a 6-foot-thick wall and gain access to the basement vault where the safe deposit boxes were, police said at the time.
The Metropolitan Police said its officers had worked "relentlessly" over the past six weeks to track down those responsible and recover the stolen goods.
"An intense investigation has been undertaken to ensure the victims, the individual box owners, the small businesses and the wider Hatton Garden community can get justice," it said.
However, the force acknowledged that its initial response to an intruder alarm triggered by the thieves at the safe deposit company had been lacking and said it was working to improve its systems.
Value of losses unconfirmed
Speaking outside New Scotland Yard, the force's headquarters, Cmdr. Peter Spindler said the processes that the Met Police have in place with alarm companies had not been followed.
"As a result of that, officers did not attend the premises when in fact they probably should have done; and for that I want to apologize," he said.
Police haven't given a precise value for what was taken. Numerous British news organizations put the value of the loss in the hundreds of thousands of pounds, but a former police official in London has speculated it could run to £200 million ($310 million), an estimate widely reported by news media.