A video covertly filmed by a train driver appears to show water pouring into the City Loop near Parliament station.

The footage, filmed sometime this year and handed to Fairfax Radio this week, purports to show water gushing into the underground tunnel about 200 metres from Parliament station.

Metro operate mobile underground pumps to ensure the Loop is clear of water.

It is unclear how serious the current problem is, or whether it is within normal operating parameters.