Overcrowding and a lack of social distancing remain a problem on Adelaide trains, despite the State Government saying increased peak-hour services have been rolled out.

Commuters on one early morning train from Salisbury were "nose to tail" according to ABC Radio Adelaide reporter Spence Denny, with the service leaving standing room only.

The lack of space comes days after South Australian Premier Steven Marshall promised an increased capacity of one train every 15 minutes during peak hour to reduce overcrowding.

Adelaide Metro's services were reduced earlier this month after a mechanical fault was identified, taking 50 of the state's 70 diesel engines out of use temporarily and forcing half-hourly trains on some lines.
Coronavirus update: Follow all the latest news in our daily wrap."My understanding is they'll all be back in service on Monday, and we'll be back to those 15-minute time zones in the peak hours on those main lines," Mr Marshall said on Friday.

SA Labor published several images on social media of passengers packed into trains on the Gawler line on Monday, but a Liberal spokesperson said trains ran every 15 minutes during peak hour on the line.