Poland on Saturday urged Britain to keep its residents safe from xenophobia as British police probed the murder of a Pole they believe could be the victim of a hate crime.

"We're counting on the British government and authorities responsible for the safety of British and European citizens, including Poles, to prevent the kind of xenophobic acts we've seen recently," Polish Foreign Minister Witold Waszczykowski said in Warsaw following talks with British counterpart Boris Johnson.

Six teenagers were arrested on suspicion of involvement in the murder of 40-year-old factory worker Arek Jozwik in Harlow, northeast of London, last Saturday. The youths are out of police custody on bail.

Investigators say they are looking into whether the killing was a hate crime, but stress the motive is still unclear.

There was an upsurge in the number of reported hate crimes around the period of the June 23 referendum in which Britons voted to leave the European Union.

Hundreds of people, many of them Poles, gathered in Harlow Saturday for a vigil to remember Jozwik, an AFP photographer at the scene said.

Many waved Polish flags and scarves and laid flowers at the scene of the killing, while the Polish national anthem was sung and a minute's silence held.

"We all agree that there is absolutely no place for xenophobia in our society," said Johnson, de facto leader of the "Leave" camp during the referendum campaign, in Warsaw.

The National Police Chiefs' Council said more than than 3,000 incidents were reported to police in England, Wales and Northern Ireland between June 16 and 30 -- an increase of 42 percent from the same period last year.

But Poland's ambassador to Britain, Arkady Rzegocki, said this week he had hoped that the situation was stabilising.

A man holds up a scarf in the crowd ahead of a minute's silence, at the shopping centre where exactly a week ago Arek Jozwik was killed Justin Tallis, AFP

Some 800,000 Poles are thought to live in Britain, one of its biggest minority groups, under EU rules allowing freedom of movement between member states. Poland joined in 2004.

Many Brexit supporters want to close Britain's borders to migrants from elsewhere in the EU while Prime Minister Theresa May has promised that immigration controls will be imposed.

"The Polish contribution to our society and our culture, and above all to our economy, is absolutely immense," Johnson added.

Waszczykowski insisted that "the huge number of Poles living in Britain constitutes an important area of our cooperation."

Britain will have to stick to the EU's freedom of movement rules until it officially leaves the bloc.