The BBC's Damian Grammaticas reports

Emergency services believe a gas heating boiler started leaking at the Crown Inn in Wentnor on the slopes of the Long Mynd in Shropshire.

The alarm was raised when pub staff found the two women, both in their 20s, slumped side by side on the floor of their guest room on Sunday morning.

The married couple staying in the room next door were discovered unconscious in bed.

They were flown to the Wirral Hospital on Merseyside by air ambulance after being given oxygen at the scene. On Sunday evening they were said to be in a comfortable condition.

Four other people, all believed to be women in their 20s, were taken to the Royal Shrewsbury Hospital suffering from the effects of carbon monoxide.

The BBC's Andrew Bomford: An investigation is underway

The police, the Health and Safety Executive and the local authority have all begun investigations.

Detective Inspector Peter Dyke said the police enquiries were concentrating on a heating boiler situated beneath the dead women's room.