Media playback is unsupported on your device Media caption Passengers at Brighton station gave their views on the RMT strike

The prime minister "strongly condemns" a five-day strike that has hit hundreds of thousands of Southern passengers, Downing Street has said.

Hundreds of trains were cancelled on the first day of the strike, which is over plans for drivers, rather than conductors, to operate carriage doors.

The RMT union said safety was the key issue and support was "rock solid".

A spokesman for Theresa May said the action was "only going to cause more disruption and misery".

946 trains cancelled

Southern said it was operating nearly 60% of its regular timetable and nine in 10 of those trains were "running on time".

A spokeswoman admitted 946 of its normal 2,242 services would be cancelled each day during the stoppage, which began at 00:01 BST and is due to end at 23:59 BST on Friday.

Southern's parent company Govia Thameslink (GTR) thanked passengers for their "patience and understanding" and called on the RMT "to let this strike be the last".

Southern rail strike: Your rights

But Shadow Transport Secretary Andy McDonald blamed the government for the strike, understood to be the longest on British railways since 1968.

Mr McDonald said: "The country's biggest rail franchise is failing. Passengers are enduring the worst delays in the country, fares are up 25% and promised investment looks further away than ever.

"Yet the Tory government seems more interested in pursuing an ideological dust-up with rail unions than improving abysmal passenger services."

Image caption Commuters at Brighton station were advised to expect "very busy" trains

Live updates on Southern strike

Latest disruption information on BBC Travel

The RMT has held a series of one-day strikes since April after balloting 393 members.

Last month, Southern, which operates services from Sussex and Surrey to London, Kent, Hampshire and Buckinghamshire, brought in a reduced timetable in response to continued cancellations and delays, blaming issues with crew availability.

The company has arranged queuing systems at some busy stations to cope with the evening rush, which earlier was made more challenging by a broken-down London-to-Brighton train at Gatwick Airport which forced passengers on to another service.

A rail users' group in east Surrey said the latest disruption was "another heavy slap in the face for poor, tired and frustrated commuters".

In a statement, the Reigate, Redhill and District Rail Users' Association said: "Members of the RMT have guaranteed jobs, a good salary and a reasonable work/life balance, whereas the long-suffering commuters are under threat of losing jobs, losing salary, losing holiday and being unable to get home to their families.

"The RMT leadership shows utter contempt to rail users by ruining their daily lives for the honour of pushing a button to close train doors."

Image copyright Corinne Graehame Image caption Corinne Graehame is a disabled passenger who uses a mobility scooter and often travels on Southern.

Corinee Graehame, a disabled train user from Hastings, said: "It's very hard to get on a packed train when people are already sitting in disabled seats and staff don't want to help with a ramp.

"I have been told to just sit in my scooter, if I can get on a train."

Photographer Hannah Kenyon, 27, has paid about £100 to hire a car for the week - on top of her usual £55.40 train fare - for her journey from Hove to Emsworth.

Image caption One commuter on 07:11 Oxted to London Bridge said passengers were trying to look after each other by creating room and squashing up together.

The Conservative MP for Lewes, Maria Caulfield, tweeted: "Judging by my inbox this morning the tide has turned against the unions in this industrial dispute."

Fellow East Sussex MP and member of the Transport Select Committee Huw Merriman has tweeted a video diary of his journey from Bexhill to Brighton via Eastbourne. He said he was "a bit disappointed Southern rail couldn't find some buses to put as a replacement service".

And Wealden Conservative MP Nus Ghani has made representations to GTR and Transport Secretary Chris Grayling about the absence of services to Uckfield, which she said was already poorly served.

"Even a misery line is better than having no line at all," she said.

Image caption Southern is running a limited service on some lines from Lewes station

A collapse in industrial relations

Analysis by BBC South transport correspondent Paul Clifton:

The situation is exactly the same today as it was five months ago. The union will not budge on having a safety-qualified guard on every train that currently has one. It will not discuss whether the driver or guard closes the train doors without that promise. And the company is not budging either.

For passengers, things could get a lot worse. More than 1,000 platform staff are currently balloting for strike action over the closure of some ticket offices and a new role of "station host".

At the same time, drivers on Southern and Gatwick Express are also holding a separate strike ballot. Those results will be known by the end of the month.

On top of that, Southern still has a chronic shortage of train crew. That is why it has an emergency timetable, cancelling 340 trains a day even when there is no strike. And that emergency timetable will continue for at least another month.

Image copyright Press Association Image caption RMT picket line opposite Victoria Station in London

Transport campaigners plan to hand in a "six-foot letter" to new Rail Minister Paul Maynard on Wednesday, urging him to "listen to passengers, freeze fares and pay compensation".

RMT general secretary Mick Cash said: "This action has been forced on us by the arrogance and inaction of Govia Thameslink and the government who have made it clear that they have no interest in resolving this dispute or in tackling the daily chaos on Southern.

‎"Our fight is with the company and the government who have dragged this franchise into total meltdown. We share the anger and frustration of passengers and we cannot sit back while jobs and safety are compromised on these dangerously overcrowded trains."

The RMT has called on GTR to match terms offered by ScotRail in a similar dispute.

Media playback is unsupported on your device Media caption The RMT union's Paul Cox says they are "genuinely sorry" about the strike

GTR chief executive Charles Horton said the RMT action was "completely unacceptable, unjustified and unnecessary" and he apologised for the "inconvenience and disruption to passengers' lives as a result".

He said the union rejected GTR's eight-point offer "out of hand".

Media playback is unsupported on your device Media caption Govia Thameslink chief exec Charles Horton says changes are needed to improve services

No trains are running between:

Havant - Chichester

Horsham - Dorking

Redhill - Tonbridge

Haywards Heath - Seaford (buses between Lewes and Seaford)

Oxted - Uckfield

Preston Park - Hove

Eastbourne - Ashford International via Hastings (peak hours buses between Hastings and Ashford International)

Tulse Hill - West Norwood

Other lines have a "significantly reduced service" between 07:30 and 18:00 only:

Chichester - Three Bridges

London Victoria - Three Bridges

Brighton - Eastbourne

London Bridge - East Grinstead

Brighton - Littlehampton/Bognor Regis

See Southern rail's map of revised services during the strike