It is believed to be the longest rail strike since 1968, with Southern-parent Govia Thameslink involved in a dispute with the RMT over plans for drivers to operate doors on new trains using CCTV.
Rail travellers angry at a five-day walkout affecting Southern Rail trains have clashed with staff and striking workers at picket lines.
Southern's passenger services director Alex Foulds said: "We would like to thank our passengers for the patience and understanding they are showing during this unnecessary strike, and we apologise to them for the disruption they are experiencing today".
"The RMT is causing yet more misery for our passengers and we call on them to let this strike be the last".
Govia Thameslink Railway's (GTR) proposals to settle the guards/conductors' dispute led by the RMT union at ACAS were not successful and the strike commences on Monday 8 August and runs to Friday 12 August inclusive.
Southern said its strike timetable was still running well as the evening peak approached, with no issues at stations and 88.5% of services on time.
Southern expects to run almost 60% of its normal timetable during the strike period using extra conductors and there will be extra staff at stations to assist passengers. The RMT, which is fighting a similar battle with Scottish railways operator ScotRail, says the move risks passenger safety.
New contracts changing the guards' roles are expected to take effect in a fortnight's time.
"The Prime Minister strongly condemns the strike action", the spokeswoman said. No more talks are planned.
And ASLEF, the train drivers' union, is to ballot staff over "a breakdown in industrial relations". The dispute is about GTR imposing driver rosters.
Long-running talks broke down when rail bosses refused to suspend the introduction of the new plans.
On Wednesday protesters are to march on the Department for Transport, setting off from Victoria Station at 5.30pm.
One commuter said: "If Southern Rail was stripped of its franchise could new company take over and hire new drivers/conductors on lower wages?" Our On-Board Supervisors will also be able to work on any service, which means more efficient working and fewer cancellations for our passengers.
"The DfT must ensure passengers receive greatly improved services and appropriate compensation, to enforce franchise commitments and to agree mechanisms so performance levels do not fall to such levels again".
It can't just be us who are a little confused about why exactly Southern Railway passengers are facing a whole week of travel chaos.
Southern's temporary timetable will continue for at least three weeks after the strike ends but with one major addition to the last month.