Heavy rain has slammed into Brisbane, causing flash flooding and traffic chaos across the city, with reports of over 55mm falling in an hour.

Authorities are warning of long delays on the Ipswich Mwy between Redbank and Darra due to heavy rain causing issues in both directions.

There is also congestion on the Pacific Motorway from Loganholme to Rochedale, and reports of flash flooding at Goodna.

A severe thunderstorm warning is active for parts of Ipswich, Logan, Redland City and Brisbane City Council areas.

The Bureau of Meteorology warned that, at 11.55am, severe thunderstorms were detected on the weather radar near Ipswich and Tingalpa Reservoir.

These thunderstorms are slow moving. and are forecast to affect Camp Hill by 12.25 pm and Manly by 12.55 pm.

Leslie Harrison Dam recorded 55mm in the hour to 12.35pm.

Heavy rainfall that may lead to flash flooding is likely.

Inala has recorded 41mm in under 30 minutes to 11.55pm.

It comes after the Bureau of Meteorology earlier warned of large, slow-moving and unpredictable storms that could impact southeast Queensland across Thursday.

Those cells could produce thunderstorms, large hail, damaging winds and flash flooding.

"The large cells are very slow moving, which means a significant area is exposed to the potential of these conditions, however, it is likely that not all of the regions will be impacted," the Bureau of Meteorology warned.

"In the morning there was a gap for the central Brisbane area, with both the sunshine and gold coasts receiving heavy rainfall, but very little falling near the CBD.

"Concentrated heavy rainfall is likely this afternoon heading into the evening along with some damaging conditions possible for many of these areas where we have issued the warnings."