Three police officers have been taken to hospital after ammonia was thrown at them.
One of the officers received treatment for a burn to his eye, and the other two were discharged.
It follows an incident when the police received reports of a disturbance in the Muswell Hill area of Newcastle.
At 11.57pm on Friday officers arrived at an address to make an arrest, and the chemical substance was thrown at them.
A man and a woman have been arrested.
"The safety of our officers is paramount and this sort of behaviour towards them is completely unacceptable.
"We take these matters very seriously and we will take robust action on anyone responsible. We will also ensure the officers involved receive the suitable welfare needs required to support them."
More top news
A look ahead at the Bank Holiday forecast for the Tyne Tees region.
Do you want to Leave or Remain in the European Union? That's the question facing everyone in the country. But what do young people think?
Remain or Leave? The impact on agriculture in the North East