The Monaco Grand Prix has been cancelled and the Dutch and Spanish races have been postponed due to the coronavirus outbreak.
The first four races in Australia, Bahrain, Vietnam and China had already been called off due to the pandemic.
The sport's governing body, the FIA, says it expects the 2020 season to begin "as soon as it is safe to do so after May".
Monaco organisers said it was "not possible" to rearrange a date.
It is still hoped the other two races can be rescheduled later in the year.
In a joint statement with F1 and the race promoters, it said decisions were taken "to ensure the health and safety of travelling staff, participants and fans".
The decision comes at the end of a seismic week of developments in F1.
The season-opening Australian Grand Prix last weekend had to be called off after a McLaren team member tested positive for coronavirus in Melbourne and a total of 16 members of that team had to go into quarantine.
The decision to call off the following races in Bahrain and Vietnam followed within a few hours, while the Chinese Grand Prix had already been postponed in February following the virus outbreak in that country.
Since then, the sport has shifted its "summer break" forward to March and April to free up time to fit as many races into this year as possible once the season can resume, and the teams, F1 and the FIA have agreed to delay the introduction of a major set of rule changes by a year until 2022 to keep costs down.
A year has to have a minimum of eight grands prix to count as a World Championship.
F1 chairman and chief executive officer Chase Carey said: "There was full support for the plans to reschedule as many of the postponed races as possible as soon as it is safe to do so.
"F1 and the FIA will now work to finalise a revised 2020 calendar and will consult with the teams, but as agreed at the meeting the revised calendar will not require their formal approval.
"This will give us the necessary flexibility to agree revised timings with affected race promoters and to be ready to start racing at the right moment.
"Formula 1 remains fully committed to launching a 2020 season as soon as possible."
F1 has a working plan to try to start the season with the Azerbaijan Grand Prix on 7 June, but this may not be possible given the rapidly escalating coronavirus problem around the world.
Bosses are considering all possibilities - it is likely races will be run on a number of consecutive weekends, and be grouped together geographically as much as possible to facilitate that approach.
And some races are more likely than others to fall by the wayside as the calendar shifts.
The most vulnerable are the Spanish, Brazilian, Chinese and Australian Grands Prix.