Google’s Gmail service was completely blocked in China for a fourth day running on Monday, marking an escalation of the disruption that has hit the webmail service since the middle of this year.

Following a steady decline for the company’s Chinese search service since 2010, when it was relocated to Hong Kong, email had until last week been among the company’s most actively used services in China. According to traffic data published by Google, it saw a steady rise in popularity in the second half of this year, despite persistent disruption.

The company reported on Monday that Gmail was still unavailable in China, four days after it first noticed a sudden collapse in traffic. “We’ve checked and there’s nothing technically wrong on our end,” it said in a statement.