Tuesday's Sydney train meltdown has been described as "an act of God" by New South Wales Transport Minister Andrew Constance, who says furious commuters will not get a refund.

Key points: The Minister has asked bureaucrats to explain Tuesday's network meltdown

The Minister has asked bureaucrats to explain Tuesday's network meltdown He says frustrated customers will not receive refunds

He says frustrated customers will not receive refunds The Opposition Leader has described Sydney's train system as "third world"

Mr Constance has issued a please explain to Sydney Trains bureaucrats about why the system has been "a mess" for the past 48 hours.

Sweaty commuters in the Harbour City have vented their frustration about the issue on social media, complaining of widespread delays and overcrowded carriages.

Travellers were also turned away from certain platforms at Central and Wynyard due to significant overcrowding.

"It's an act of God when you have three lightning strikes take out substations, train routes and signalling," Mr Constance said.

"Coupled with the fact that we've had to put more trains and more services on to cater for Sydney's growth, I'm not shying away from apologising for what happened in the last 48 hours, but the train timetable has operated well for the past month and a half."

Commuters were packed in at Strathfield station yesterday afternoon. ( ABC News: Nour Haydar )

So far, a combination of a higher-than-expected number of drivers on sick leave, wild weather and an increase in patronage have been blamed for the delays.

Mr Constance said he had asked Sydney Trains bosses Howard Collins and Rodd Staples to report to him in the next fortnight on the delays.

There were significant delays on the network on Monday and Tuesday, and several minor delays on Wednesday morning.

The NSW Government last month overhauled the timetable, adding an extra 1,500 services per week.

Sorry, this video has expired 'Perfect storm' caused train delays: Minister

However, Mr Constance said a busier network was not the reason behind the delays.

"When we have a major incident, as we've seen under any timetable, we can see major disruptions and it has been a mess the last 48 hours," he said.

"I expect the next 48 hours to be better and we'll continue to work at it."

Train service 'third world'

NSW Opposition Leader Luke Foley said the disruptions and delays were unacceptable.

"Thousands of people jammed in like sardines, held back by staff and barriers, held back by police with announcements begging people to leave the station and find another way home," he said.

"This is a train service reminiscent of a third-world city."

Mr Constance said Sydney Trains normally catered for about 40 drivers being off sick.

On Tuesday, Sydney Trains estimated between 65 and 70 train drivers were off due to illness, however the Transport Minister said he did not want to comment on that issue.

"The reality is that, you know, people get sick. I mean, I've been unwell myself in the last fortnight," he said.

Many of Sydney's train lines were experiencing indefinite delays yesterday. ( ABC News: Clare Blumer )

He said more than 200 train drivers had been employed since 2016, and 18 new drivers would start work in February.

However, Sydney Trains and the NSW Government appears to be at odds with their drivers over staffing numbers.

One driver, who did not want to be named, described staff shortages as "severe" and claimed there were now no emergency staff available to cover people who were sick.

They described the NSW Government as being "solely responsible" for the "chaos".

Mr Collins said he would investigate what went wrong over the past 48 hours.

"It's not guaranteeing that there'll be a perfect service every day next week — there may well be other days when we've got to work hard to get people home," he said.