Warnings about ice on Welsh roads were issued

They included a 10-vehicle accident on the A4059, the Trecynon by-pass in Aberdare, just after 0600 GMT.

Police say about 30 accidents occurred on the A470 in south Wales and 10 people were taken to hospital with minor injuries.

The A470 was closed in both directions.

The southbound A470 between Pontypridd and Abercynon was blocked at about 0700 GMT, and collisions on the northbound stretch led to closure between Treforest and Pentrebach, Merthyr.

Police advised people to delay their journeys and to stay at home until the A470 was re-opened. The road was opened again shortly after 0900 GMT.

The condition of roads in Aberdare led to Blaengwawr Comprehensive School being closed for the day.

There was a five-car pile-up on the northbound carriageway of the A483 just outside Wrexham just after 0800 GMT.

North Wales Fire Service said no-one was trapped in the crash but two people suffered minor injuries.

Dyfed-Powys Police said all roads were open, but black ice caused more than a dozen accidents on the A40 between Carmarthen and St Clears.

A lorry jack-knifed at Pontargothi, partially blocking the road.

They warned drivers to take extra care.

A spokesman for Rhondda Cynon Taf council said the roads throughout the area were gritted on Thursday night.

"However, during the early hours of the morning, unforecast rain washed the salt away and then froze on the roads," he added.

"South Wales Police closed the A470 for a short time as a safety precaution.

"All gritters and available staff were mobilised as soon as possible this morning to work to improve the situation."

The rush-hour traffic problems followed a Wales-wide warning of icy roads issued by the Met Office at 0650 GMT.