Online grocer Ocado delivered another double-digit hike in sales and said it notched up 250,000 orders in a week for the first time.

The group posted a 15.3% rise in group gross sales - which is boosted by its deal to handle online deliveries for Big Four supermarket Morrisons - to £312.4 million for the 12 weeks to February 21, while retail sales lifted 13.8%.

Ocado said it hit its weekly orders milestone since the end of its first quarter, despite ongoing tough trading in the grocery sector, which is gripped by a fierce price war with discounters Aldi and Lidl.

But the size of its average order slipped 2.9% to £111.41 during the first quarter in a sign of the pressures in the sector.

Tim Steiner, chief executive of Ocado, said: 'We are pleased with the steady progress in our business, maintaining double-digit sales growth in a retail environment that remains challenging.'

Its trading update comes amid concerns over the impending threat from US online giant Amazon after it struck a deal last month with Morrisons.

The tie-up will see Amazon offer 'hundreds' of Morrisons products - including fresh and frozen food - through its food delivery service Amazon Pantry and its subscriber service Amazon Prime Now.