Four people have been killed in a road crash involving a tanker, a car and a van.
Dyfed-Powys Police said two men and two women died following the crash on the A44 between Llangurig and Ponterwyd.
An infant girl was seriously injured and has been taken to University Hospital of Wales Cardiff, police said.
A police spokesman said: " Dyfed-Powys Police remain at the scene of a serious RTC on the A44 between Llangurig and Ponterwyd. The collision occurred at approximately 2.55pm this afternoon, and a tanker, a car and a van were involved.
"We can now confirm that tragically two men and two women sustained fatal injuries in the collision, and a female infant has been taken to the University Hospital of Wales Cardiff in a serious condition.
"Next of kin have been informed and are being supported by specialist officers.
"The road remains closed and is likely to remain closed for some time - diversions are in place."
A spokeswoman for Mid and West Wales Fire and Rescue Service said two fire engines were sent to the scene of the crash after a call was received at 3.01pm.
The appliances, from Aberystwyth and Llanidloes, made the vehicles involved in the accident safe.
Firefighters left the scene at 8.29pm.
It is believed those who died are from the same family. The girl, who has head injuries, was airlifted to hospital.
The A44 is one of the main roads in mid Wales and links Ceredigion with Powys. A 21 mile stretch of the road is closed.
A spokeswoman for Wales Air Ambulance said: "Our Welshpool-based crew responded to a road traffic collision on the A44 near Pantmawr today, where they treated and airlifted a female child to UHW Cardiff."
She said the air ambulance was called at 3.10pm and arrived at 3.24pm.
The helicopter left the scene carrying the young girl at 3.43pm and arrived at the University Hospital of Wales at 4.15pm.
Eluned Thomas, from Eisteddfa Gurig farm about two miles away, called the emergency services after a woman alerted her to the accident.
She said the tanker was travelling towards Aberystwyth and she believed the other vehicles were going in the opposite direction.
Mrs Thomas said road traffic accidents "happen all the time" in the area.
"It's a windy road the A44. It's a trunk road. It's a very important and busy main road," she added.
She said the woman asked her to call for help because there was no mobile phone coverage at the crash site.