The latest numbers from a commercial real estate firm show Calgary's downtown office market continues to diverge from the national trend as it hits its highest vacancy rates in more than 30 years.

CBRE Canada estimates the city's downtown office vacancy rate ended the first quarter at 20.2 per cent, almost twice as high as the 11.8 per cent vacancy rate in the same period a year ago.

In its first-quarter update released today, CBRE says it's the first time since 1983 that more than one fifth of office space was on offer, and the city is on track to hit a new record above the 22 per cent rate reached in the early 1980s.

CBRE says with rental rates down 28 per cent in a year, prices have dropped to an average of $20.97 per square foot for top-tier class A office space from $29.23 in the same quarter a year ago.

The trend contrasts with other major Canadian markets, with Toronto's downtown office vacancies up only slightly in the quarter to 5.3 per cent, while Vancouver's dropped to 8.8 per cent and Montreal's was down to 10.8 per cent, according to CBRE.

Calgary's office market has been hit hard as oil and gas companies continue to cut jobs and consolidate office space due to low crude prices.