Two Swiss mountaineers have landed a small plane less than 400 metres from the top of Mont Blanc before heading for the summit with police in pursuit.

The pair landed the aircraft 4,450 metres (14,600ft) up the mountain in the French Alps on Tuesday in an incident described as an unprecedented “provocation” by Eric Fournier, the mayor of the nearby Chamonix resort.

“It constitutes an intolerable attack on the high mountain environment and on all existing protective measures,” he said.

Lt Col Stephane Bozon, who heads the gendarmerie’s mountain rescue service in Chamonix, told Agence France-Presse that police saw the plane on the east face of Mont Blanc. Officials said the area is not an authorised landing zone.

The two climbers were equipped with ropes and crampons and had already started climbing towards the summit when they were intercepted by police and asked to turn back, according to local media.

Bozon said were considering what offence may have been committed.

Thousands of climbers visit Mont Blanc during summer, aiming to reach the 4,809-metre summit. Officials have been grappling with an increase in the number of tourists hoping to scale the mountain, with some attempting it without sufficient equipment or experience. It has led to some people camping illegally and concerns over water availability and problems with waste disposal.

• This article was corrected on 21 June 2019. Europe’s highest mountain is generally considered to be Mount Elbrus in Russia (at 5,642m), rather than Mont Blanc as the article stated.