Earlier, Nats said the eruption, which has caused the closure of the UK's airspace since Thursday, had worsened.
It said: "The volcano eruption in Iceland has strengthened and a new ash cloud is spreading south and east towards the UK."
The situation is due to be reviewed again at 1500 BST.
Newcastle Airport reopened at 0700 BST, allowing a few flights to land and leave.
A flight from Aberdeen landed at the airport 0939 BST and a return service took off at about 1200 BST.
A Jet2.com plane left Newcastle at 1100 BST on a rescue mission to pick up 229 stranded passengers in Sharm el Sheikh, Egypt.
Ian Doubtfire, managing director of Jet2.com, said: "It is our absolute priority to get our passengers back to the UK as soon as we possibly can and we are currently in the process of a wide-scale repatriation programme to bring our passengers home."
British Airways said 12 long-haul flights were currently en route to Heathrow, from Beijing, Singapore and the west coast of the US.
A spokeswoman said they had contingency plans for each flight if Heathrow was still closed.
Ferry company Norfolkline was carrying 49-seat coaches for foot passengers on some of its Dover-Dunkirk crossings for a second day.
Coaches will also be accommodated again on Wednesday.
Some schools in England have been forced to close as teachers and pupils remain stranded abroad.
A union is fighting moves to dock the pay of Devon teachers who are unable to attend school because of the flight ban.
Devon County Council warned pay could be docked, although added it was reviewing the policy "in light of the extreme circumstances".
Elsewhere, a mother of a soldier killed in Afghanistan is unable to get to the inquest of her son due to the flight ban.
British troops are returning from Afghanistan on HMS Albion
Lorraine McClure is in Gran Canaria and is desperate to get to Trowbridge, Wiltshire, where the inquest is resuming into the death of Pte Aaron McClure.
Pte McClure and two other British soldiers were killed by a 500lb (227kg) bomb dropped by a US aircraft.
Mrs McClure's solicitor appealed for help to get her back as soon as possible.
British troops stranded in Spain are being taken home by warship HMS Albion.
The Plymouth-based ship is bringing home 250 soldiers from 3rd Battalion The Rifles who have been deployed in Afghanistan for six months.
HMS Albion is also carrying 200 British civilians.
Two other Royal Navy ships are on standby for similar rescue missions.
In Birmingham, the airport chaos has not stopped the European Gymnastics Championships from going ahead.
Organisers delayed the start by 24 hours and made arrangements to collect competitors from UK ports and take them to Birmingham.
A Foreign and Commonwealth Office 24-hour consular helpline has been set up on 020 7008 0000 for people stuck abroad.
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