Homes are being evacuated as flooding has brought "chaos" to roads in north Wales, with people rescued from cars and vehicles left stranded. The A55 has been closed between junction 11 for the A5 and junction 15 at Llanfairfechan. The A5 was closed near Betws-y-coed, and in Powys, the A487 Dyfi Bridge at Machynlleth has also been shut. Coastguard teams are helping people from homes near Beaumaris castle, on Anglesey, after its moat overflowed. Natural Resources Wales (NRW) has issued 12 flood warnings for north, mid and west Wales, along with dozens of alerts. The Met Office has stepped up its "be aware" warning to "be prepared", which is in place for north west Wales until 23:00 GMT Saturday. Supt Nigel Harrison of North Wales Police said it had received a "high level" of flood-related calls and the force was working with other agencies to safeguard the public. "Every effort is being made to ensure all the major road networks are re-opened as soon as possible and people living in the affected areas need to heed the warnings and only travel when it is absolutely necessary," he said. "We are in close liaison with Natural Resources Wales to ensure the necessary steps are taken should any further evacuation be required." "Flood water can be extremely dangerous, and people should not attempt to walk or drive through it unless instructed by the emergency services," he added. Earlier on Saturday, a North Wales Police spokesman said problems were first reported on the A55 and A5 roads late on Christmas Day and they were likely to be closed for 24 hours. He said the force had received reports of floating cars and some people had to be rescued, adding: "It's chaos at the moment." In Denbighshire, temporary defences have been deployed in St Asaph to protect homes in the Roe Park area as heavy rain overnight has caused the River Elwy to rise. Donna Littlechild of NRW said: "Unfortunately, the festive period did not bring any respite from the recent wet weather and we have been monitoring the rivers and taking action to warn people and prepare our defences. "We're asking people to take care near water and to keep an eye on our website where flood alerts and warnings are updated every 15 minutes. "We are also asking people to take the advice of the emergency services and to keep themselves and their friends and family safe."