South Central Ambulance Service pleaded for people to only dial 999 in a life-threatening emergency.

It said a surge in demand since May had been exacerbated by growing Covid-related pressures in October.

The service said some patients would have to wait longer for an ambulance to reach them.

On Saturday evening the service tweeted: "Please, please support us by using our services wisely, we're here for life threatening illnesses and injuries."

It said several factors were to blame including GP waiting-list backlogs, ambulance queues at hospitals and people who had not been able to get medical help during the pandemic.

David Lynn saw 21 ambulances queuing at the Queen Alexandra Hospital in Portsmouth at about 03:45 GMT.

He said patients seemed to be "stuck on board" with some having been there for hours.

Phil Pimlott, the service's assistant director of operations, said: "We are extremely busy but are working well with all of our partners at this very challenging time.

"Overnight our staff worked very hard to minimise the time taken to hand patients over to the care of local hospitals."

The service said 999 calls were 13% above levels in 2019 while demand from the NHS 111 service, for less urgent incidents, was 30% more than expected.

On Wednesday, the Association of Ambulance Chief Executives said the sector was experiencing "some of the highest levels of emergency activity in its history".

Managing director Martin Flaherty said: "This is regrettably leading to delays in the sector's ability to respond to some patients."

In May, South Western Ambulance Service also declared a critical incident.

According to the NHS, a declaration of a critical incident allows all health and care organisations to work together and focus on resolving the situation.

South Central covers the counties of Berkshire, Buckinghamshire, Hampshire and Oxfordshire, as well as operating non-emergency patient transport services in Sussex and Surrey.